Staggered full partitioned snapshots

ABSTRACT

Methods and systems for backing up and restoring different point in time versions of a virtual machine, a real machine, an application, a database, or a set of electronic files using a plurality of independently managed snapshot chains are described. The different point in time versions of the data being backed-up may be stored using two or more snapshot chains corresponding with two or more data partitions of the data being backed-up. Over time, additional full image snapshots may be acquired from an external server or generated locally by a storage appliance to limit the snapshot chain lengths and to limit the aggregate block chain lengths for the snapshot chains. Acquisition and generation of the additional full image snapshots may be staggered across different data partitions to limit computational and storage costs per snapshot.

BACKGROUND

Virtualization allows virtual hardware to be created and decoupled fromthe underlying physical hardware. For example, a hypervisor running on ahost machine or server may be used to create one or more virtualmachines that may each run the same operating system or differentoperating systems (e.g., a first virtual machine may run a Windows®operating system and a second virtual machine may run a Unix-likeoperating system such as OS X®). A virtual machine may comprise asoftware implementation of a physical machine. The virtual machine mayinclude one or more virtual hardware devices, such as a virtualprocessor, a virtual memory, a virtual disk, or a virtual networkinterface card. The virtual machine may load and execute an operatingsystem and applications from the virtual memory. The operating systemand applications executed by the virtual machine may be stored using thevirtual disk. The virtual machine may be stored (e.g., using a datastorecomprising one or more physical storage devices) as a set of filesincluding a virtual disk file for storing the contents of the virtualdisk and a virtual machine configuration file for storing configurationsettings for the virtual machine. The configuration settings may includethe number of virtual processors (e.g., four virtual CPUs), the size ofa virtual memory, and the size of a virtual disk (e.g., a 2 TB virtualdisk) for the virtual machine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A depicts one embodiment of a networked computing environment.

FIG. 1B depicts one embodiment of a server.

FIG. 1C depicts one embodiment of a storage appliance.

FIG. 1D depicts one embodiment of a portion of an integrated datamanagement and storage system that includes a plurality of nodes incommunication with each other and one or more storage devices.

FIGS. 2A-2K depict various embodiments of sets of files and datastructures associated with managing and storing snapshots of virtualmachines.

FIG. 3A is a flowchart describing one embodiment of a process formanaging and storing virtual machine snapshots using a data storagesystem.

FIG. 3B is a flowchart describing one embodiment of a process fordetermining the type of snapshot to be stored using a data storagesystem.

FIG. 3C is a flowchart describing one embodiment of a process forrestoring a version of a virtual machine using a data storage system.

FIG. 4A depicts one embodiment of sets of electronic files for capturingdifferent point in time versions of protected data.

FIG. 4B depicts one embodiment of a snapshot chain being split into twosnapshot sub-chains.

FIG. 4C depicts another embodiment of a snapshot chain being split intotwo snapshot sub-chains.

FIG. 4D depicts one embodiment of two snapshot sub-chains being splitinto three snapshot sub-chains.

FIG. 4E depicts one embodiment of two snapshot sub-chains beingconsolidated into a consolidated snapshot chain.

FIG. 4F depicts one embodiment of converting a portion of a snapshotchain into two or more snapshot sub-chains.

FIG. 4G depicts one embodiment of consolidating snapshot sub-chainsassociated with a subset of backed-up versions of protected data into asingle snapshot chain.

FIG. 4H depicts one embodiment of consolidating two snapshot chains intoa single snapshot chain.

FIG. 4I depicts one embodiment of the two snapshot sub-chains of FIG. 4Ain which snapshot sub-chain operations have been independently performedon the two snapshot sub-chains.

FIG. 4J depicts one embodiment of four snapshot chains that correspondwith four data partitions comprising a set of electronic files to bebacked-up.

FIG. 5A depicts one embodiment of four snapshot chains correspondingwith a set of electronic files that have been partitioned into fourdifferent data partitions.

FIG. 5B depicts one embodiment of four snapshot chains correspondingwith a set of electronic files that have been partitioned into fourdifferent data partitions.

FIG. 5C depicts one embodiment of a snapshot chain depicted in FIGS.5A-5B.

FIG. 5D depicts one embodiment of a snapshot chain in which a secondfull image snapshot has taken the place of an incremental snapshot.

FIG. 5E depicts one embodiment of a snapshot chain in which a secondfull image snapshot has been stored corresponding with a point in timeversion of the set of electronic files at time T6.

FIG. 5F depicts one embodiment of a snapshot chain with an incrementalsnapshot that includes redundant data blocks.

FIG. 5G depicts one embodiment of a snapshot chain that includes anincremental snapshot with redundant data blocks.

FIG. 5H depicts one embodiment of a snapshot chain that includesstaggered full image snapshots and an incremental snapshot withredundant data blocks.

FIG. 5I depicts one embodiment in which a data partition has beenpartitioned into two sub-partitions.

FIG. 5J depicts another embodiment in which a data partition has beenpartitioned into two sub-partitions.

FIG. 6A is a flowchart describing one embodiment of a process foracquiring full image snapshots.

FIG. 6B is a flowchart describing an alternative embodiment of a processfor acquiring full image snapshots.

FIG. 7A is a flowchart describing one embodiment of a process forgenerating and storing full image snapshots.

FIG. 7B is a flowchart describing another embodiment of a process forgenerating and storing full image snapshots.

FIG. 7C is a flowchart describing one embodiment of a process forgenerating and storing full image snapshots based on an aggregate blockchain length.

DETAILED DESCRIPTION

Technology is described for backing up and restoring different point intime versions of a virtual machine, a real machine, an application, adatabase, or a set of electronic files using a plurality ofindependently managed snapshot chains. In some cases, the entire dataset being backed-up (e.g., a set of electronic files) may be partitionedinto two or more data partitions such that each partition is less than athreshold data size (e.g., each data partition is less than 10 TBs ofdata). The different point in time versions of the data set beingbacked-up may be captured on a periodic basis (e.g., every four hours)and stored using two or more snapshot chains corresponding with the twoor more data partitions of the data set being backed-up. Each of thesnapshot chains may include a full image snapshot (or a base image) andone or more incremental snapshots (e.g., a forward incremental snapshot)that derive from the full image snapshot. Each incremental snapshot maycomprise data changes relative to the full image snapshot. The datachanges may be represented using one or more changed data blocks.

In some cases, a set of electronic files (e.g., a fileset) may bepartitioned logically into a plurality of independent partitions andeach partition may correspond with a separate snapshot chain. As thetime to restore a particular point in time version of the set ofelectronic files may increase with the snapshot chain lengths for thesnapshot chains (e.g., linearly increasing with the number of forwardincremental snapshots per snapshot chain), additional full imagesnapshots may be acquired (e.g., from a server storing the set ofelectronic files) or generated (e.g., by a storage appliance backing upthe set of electronic files) over time to limit the total number ofincremental snapshots within the snapshot chains that need to be appliedto generate the particular point in time version of the set ofelectronic files. The snapshot chain length of a snapshot chain maycomprise the maximum number of incremental snapshots that derive from asingle full image snapshot for the snapshot chain. Acquisition and/orgeneration of the additional full image snapshots may be staggeredacross the different data partitions to limit the computational andstorage costs per snapshot and to limit the snapshot chain lengths persnapshot chain.

One technical issue with using snapshot chains with full image snapshotsthat comprise large file sizes (e.g., larger than 50 TB) is thatperformance of some data storage operations, such as a consolidationoperation or a rebasing operation, may be time consuming or may not bepossible if the amount of available disk space is less than a thresholdamount of disk space (e.g., the amount of available disk space is lessthan 5 TB). A threshold amount of disk space may be required insituations where the original snapshot chain (or blob-chain) needs toremain available while a consolidation operation or rebasing operationis generating a new full image snapshot. A consolidation operation maybe used to combine multiple consecutive incremental snapshots in asnapshot chain into a single snapshot. A rebasing operation may be usedto move the full image snapshot for a snapshot chain to (or closer to)the most recent snapshot within the snapshot chain. One benefit ofstoring a data set being backed-up using a plurality of independentlymanaged snapshot chains that limit the size of the full image snapshotsper snapshot chain to be less than a threshold data size (e.g., lessthan 5 TB) is that working-copy during reversals and consolidations maybe less of a problem in data storage clusters with high storageutilization. Moreover, each of the independently managed snapshot chainsmay be replicated in parallel and read from or written to in parallel,thereby improving read and write performance.

Over time, the snapshots in a snapshot chain may be archived using anarchival data store (e.g., an NFS datastore), cloud storage, objectstorage (e.g., data storage that manages or stores data as objects), orblock storage. In some cases, disk space within the archival data storemay be reclaimed by either consolidating or merging consecutive expiredsnapshots or by deleting expired snapshots. In other cases, the archivedsnapshots may be archived to an archival data store that does not havethe ability to easily compute or generate full image snapshots. In thesecases, rather than archiving an incremental snapshot corresponding witha particular snapshot, a full image snapshot of the particular snapshotmay be generated and transferred to the archival data store instead. Thetransfer of the full image snapshot may allow a chain of dependenciessupporting expired snapshots to be broken and for the expired snapshotsto be deleted or consolidated on the archival data store. The generationof full image snapshots may be performed periodically in order to reducethe size of the dependency chains for the archived snapshots. Onebenefit of reclaiming disk space by consolidating and/or deletingexpired snapshots is that available disk space may be increased and thecosts associated with storing the archived data may be reduced.

In one embodiment, a set of electronic files may be partitioned into twoor more sets of files including a first set of files and a second set offiles. The set of electronic files may comprise numerous files (e.g.,40K files) stored across one or more storage devices that are split orpartitioned based on the logical size or physical size of the files. Inone example, the set of electronic files may be sorted lexographicallyand then partitioned such that each partition comprises at most 2 TBs ofdata. Each partition may map to a directory. Each partition maycorrespond with a snapshot chain. The set of electronic files may beidentified using various search criteria. The search criteria mayutilize wildcard characters or regular expressions to find files withmatching filenames or other attributes. In this case, the set ofelectronic files may not necessarily correspond with all files storedwithin particular folders or directories and may instead comprisesubsets of files stored within the folders or directories that match aspecified pattern. In one example, the set of electronic files may beacquired from a hardware server. The first set of files may be backed-upusing a first snapshot chain and the second set of files may bebacked-up using a second snapshot chain. Once the snapshot chain lengthfor the first snapshot chain reaches a threshold limit (e.g., has morethan 100 incremental snapshots that depend from a full image snapshotfor the first snapshot chain), a new full image snapshot may be acquiredor generated in order to begin a new snapshot chain; in this case, thefirst snapshot chain may be broken and subsequent snapshots of the firstset of files may be stored as incremental snapshots that derive from thenew full image snapshot or include data changes that are relative to thenew full image snapshot.

In some embodiments, the acquisition and generation of additional fullimage snapshots for subsequent point in time versions of the first setof files and the second set of files may be staggered in order to reducethe burden on a host hardware server or storage device storing the setof electronic files and to reduce the overhead of generating theadditional full image snapshots at the same time. In one example, afirst additional full image snapshot for the first snapshot chaincorresponding with a first version of the first set of files may beacquired from a hardware server at a first point in time and a secondadditional full image snapshot for the second snapshot chaincorresponding with a second version of the second set of files may beacquired from the hardware server at a second point in time subsequentto the first point in time. Further, a first consolidation operation (oran operation that generates a new full image snapshot) may be performedon the first snapshot chain at the second point in time and a secondconsolidation operation may be performed on the second snapshot chain atthe first point in time. In this case, the first consolidation operationmay be performed to generate another additional full image snapshot forthe first snapshot chain by a storage appliance, such as storageappliance 170 in FIG. 1A, while the second additional full imagesnapshot for the second snapshot chain is acquired by the storageappliance from the hardware server, such as server 160 in FIG. 1A. Togenerate a full image snapshot locally on the storage appliance, thestorage appliance may allocate compute and storage resources prior toperforming an operation to generate the full image snapshot. Thus, twoadditional full image snapshots for two different partitions or twodifferent snapshot chains may be acquired and stored at the same timewhile limiting the computational and memory overhead for both thehardware server and the storage appliance.

In one embodiment, the acquisition or generation of additional fullimage snapshots from a server may be staggered upon detection that asnapshot chain length has exceeded or will exceed a threshold lengthwith the next snapshot (e.g., will be greater than ten incrementals).Prior to fetching data associated with the additional full imagesnapshots, a determination may be made as to whether any of thepartitions will have a snapshot chain length that will exceed thethreshold length; if so, then additional full image snapshots may beacquired for those partitions such that the snapshot chain length forthose partitions will not be exceeded. In another embodiment, ratherthan waiting until the snapshot chain length will be exceeded with thenext snapshot in a snapshot chain, additional full image snapshots maybe preemptively acquired or generated even before the next snapshotexceeds the snapshot chain length.

In some embodiments, the staggering of the acquisition and/or localgeneration of full image snapshots across two or more snapshot chainscorresponding with two or more data partitions may be performed inresponse to detecting that at least one of the two or more snapshotchains has reached or exceeded a maximum snapshot chain length. In oneembodiment, upon detection that at least one of the two or more snapshotchains has reached the maximum snapshot chain length, full imagesnapshots may be acquired and/or generated for Ceil(N*P) number ofpartitions, wherein N is total number of partitions of the two or moredata partitions and P is the maximum percentage of the partitions forwhich full image snapshots may be acquired and/or generated for aparticular point in time version of the two or more data partitions. Inone example, if there are ten total data partitions (e.g., N is equal to10) and the maximum percentage of the partitions for which full imagesnapshots may be acquired for a particular point in time version of thetwo or more data partitions is 30% (e.g., P is equal to 0.3), then thenumber of full image snapshots that may be acquired for the particularpoint in time version of the two or more data partitions is Ceil(8*0.3)or three full image snapshots. In another example, the number of fullimage snapshots that may be acquired for the particular point in timeversion of the two or more data partitions may be Floor(8*0.3) or twofull image snapshots.

In other embodiments, the staggering of the acquisition and/or localgeneration of full image snapshots across two or more snapshot chainscorresponding with two or more data partitions may be performedpreemptively (e.g., prior to the maximum snapshot chain lengths beingexceeded) if the snapshot chain length for at least one of the two ormore snapshot chains has reached D (e.g., the triggering snapshot chainlength that is less than the maximum snapshot chain length) equal to Cminus Ceil(1/P), wherein C is the maximum snapshot chain length and P isthe maximum percentage of the partitions for which full image snapshotsmay be acquired and/or generated for a particular point in time versionof the two or more data partitions. In one example, if the maximumsnapshot chain length for the two or more snapshot chains is 20 (e.g., Cis equal to 20) and the maximum percentage of the partitions for whichfull image snapshots may be acquired for a particular point in timeversion of the two or more data partitions is 20% (e.g., P is equal to0.2), then the triggering snapshot chain length D will be 20 minusCeil(1/0.2) or fifteen. In this case, once one of the two or moresnapshot chains has reached a snapshot chain length of fifteen, thenfull image snapshots for subsets of the two or more snapshot chains maybe acquired and/or generated per snapshot for the next five snapshots.In the case that there are ten total data partitions (e.g., N is equalto 10), then two full image snapshots (e.g., N*P is equal to two) may beacquired for each of the snapshots from the sixteenth snapshot to thetwentieth snapshot. Thus, for ten data partitions (P1, P2, P3, P4, P5,P6, P7, P8, P9, P10), at the fifteenth snapshot of the ten datapartitions the corresponding snapshot chain lengths may be(15,15,15,15,15,15,15,15,15,15), at the sixteenth snapshot of the tendata partitions the corresponding snapshot chain lengths may be(16,16,16,16,16,16,16,16,0,0), at the seventeenth snapshot of the tendata partitions the corresponding snapshot chain lengths may be(17,17,17,17,17,17,0,0,1,1), at the eighteenth snapshot of the ten datapartitions the corresponding snapshot chain lengths may be(18,18,18,18,0,0,1,1,2,2), at the nineteenth snapshot of the ten datapartitions the corresponding snapshot chain lengths may be(19,19,0,0,1,1,2,2,3,3), and at the twentieth snapshot of the ten datapartitions the corresponding snapshot chain lengths may be(0,0,1,1,2,2,3,3,4,4).

An entire data set being backed-up may be partitioned into two or morepartitions and each partition may correspond with a set of data blocks.A full image snapshot for one of the partitions may comprise a pluralityof data blocks (e.g., 1500 64 MB data blocks). In some cases, anadditional full image snapshot may be acquired or generated in order tolimit the snapshot chain length of a snapshot chain. For example, theadditional full image snapshot may be acquired from a hardware server tolimit the number of forward incremental snapshots that need to beapplied to a previously acquired full image snapshot to not more thantwenty incrementals. In other cases, an additional full image snapshotmay be acquired or generated in order to limit the maximum block chainlength for the plurality of data blocks. A block chain length for aparticular data block of the plurality of data blocks may correspondwith the number of incremental snapshots separating the most recent datachanges to the particular data block and the most recent snapshot of theplurality of data blocks. In some cases, a block chain length for afirst data block of the plurality of data blocks may correspond with anumber of incremental snapshots from a prior snapshot of the pluralityof data blocks that includes the most recent data changes to the firstblock to the most recent snapshot of the plurality of data blocks. Themaximum block chain length may comprise the greatest block chain lengthout of the block chain lengths for the plurality of data blocks. Inother cases, an additional full image snapshot may be acquired orgenerated in order to limit the aggregate block chain length for theplurality of data blocks. The aggregate block chain length may comprisethe sum of the block chain lengths for each block of the plurality ofdata blocks. One benefit of limiting the aggregate block chain length isthat the time to synthesize a full image snapshot or generate anincremental snapshot may be reduced as the number of older data blocksthat need to be read to check for data changes will be limited.

In some cases, one or more configuration parameters for a data storagesystem may be used to set the maximum snapshot chain length, the maximumblock chain length, and the maximum aggregate block chain length. Themaximum snapshot chain length, the maximum block chain length, and themaximum aggregate block chain length may be set based on an amount ofavailable disk space within one or more data storage nodes of a cluster,which may increase or decrease over time as storage nodes are added toor removed from the cluster and as files are added to or deleted fromthe cluster. In one example, if the amount of available disk space fallsbelow a threshold amount (e.g., is less than 10 TBs), then the maximumblock chain length may be increased from 50 to 100. In another example,if the amount of available disk space rises above a threshold amount(e.g., is more than 50 TBs due to the addition of one or more datastorage nodes to the cluster), then the maximum block chain length maybe decreased from 200 to 50. As the amount of available disk spacerises, the maximum block chain length may be decreased in order toimprove recovery time or access efficiency at the expense of storageefficiency. The maximum snapshot chain length, the maximum block chainlength, and the maximum aggregate block chain length may also be setbased on a prior history of data changes or based on an average datachange rate for a snapshot chain. In one example, if a threshold numberof data changes have occurred within a snapshot chain (e.g., within themost recent ten snapshots), then the maximum block chain length may beincreased from 10 to 20.

An integrated data management and storage system may be configured tomanage the automated storage, backup, deduplication, replication,recovery, and archival of data within and across physical and virtualcomputing environments. The integrated data management and storagesystem may provide a unified primary and secondary storage system withbuilt-in data management that may be used as both a backup storagesystem and a “live” primary storage system for primary workloads. Insome cases, the integrated data management and storage system may managethe extraction and storage of historical snapshots associated withdifferent point in time versions of virtual machines and/or realmachines (e.g., a hardware server, a laptop, a tablet computer, asmartphone, or a mobile computing device) and provide near instantaneousrecovery of a backed-up version of a virtual machine, a real machine, orone or more files residing on the virtual machine or the real machine.The integrated data management and storage system may allow backed-upversions of real or virtual machines to be directly mounted or madeaccessible to primary workloads in order to enable the nearinstantaneous recovery of the backed-up versions and allow secondaryworkloads (e.g., workloads for experimental or analytics purposes) todirectly use the integrated data management and storage system as aprimary storage target to read or modify past versions of data.

The integrated data management and storage system may include adistributed cluster of storage nodes that presents itself as a unifiedstorage system even though numerous storage nodes may be connectedtogether and the number of connected storage nodes may change over timeas storage nodes are added to or removed from the cluster. Theintegrated data management and storage system may utilize a scale-outnode based architecture in which a plurality of data storage appliancescomprising one or more nodes are in communication with each other viaone or more networks. Each storage node may include two or moredifferent types of storage devices and control circuitry configured tostore, deduplicate, compress, and/or encrypt data stored using the twoor more different types of storage devices. In one example, a storagenode may include two solid-state drives (SSDs), three hard disk drives(HDDs), and one or more processors configured to concurrently read datafrom and/or write data to the storage devices. The integrated datamanagement and storage system may replicate and distribute versioneddata, metadata, and task execution across the distributed cluster toincrease tolerance to node and disk failures (e.g., snapshots of avirtual machine may be triply mirrored across the cluster). Datamanagement tasks may be assigned and executed across the distributedcluster in a fault tolerant manner based on the location of data withinthe cluster (e.g., assigning tasks to nodes that store data related tothe task) and node resource availability (e.g., assigning tasks to nodeswith sufficient compute or memory capacity for the task).

The integrated data management and storage system may apply a databackup and archiving schedule to backed-up real and virtual machines toenforce various backup service level agreements (SLAs), recovery pointobjectives (RPOs), recovery time objectives (RTOs), data retentionrequirements, and other data backup, replication, and archival policiesacross the entire data lifecycle. For example, the data backup andarchiving schedule may require that snapshots of a virtual machine arecaptured and stored every four hours for the past week, every day forthe past six months, and every week for the past five years.

As virtualization technologies are adopted into information technology(IT) infrastructures, there is a growing need for recovery mechanisms tosupport mission critical application deployment within a virtualizedinfrastructure. However, a virtualized infrastructure may present a newset of challenges to the traditional methods of data management due tothe higher workload consolidation and the need for instant, granularrecovery. The benefits of using an integrated data management andstorage system include the ability to reduce the amount of data storagerequired to backup real and virtual machines, the ability to reduce theamount of data storage required to support secondary or non-productionworkloads, the ability to provide a non-passive storage target in whichbackup data may be directly accessed and modified, and the ability toquickly restore earlier versions of virtual machines and files storedlocally or in the cloud.

FIG. 1A depicts one embodiment of a networked computing environment 100in which the disclosed technology may be practiced. As depicted, thenetworked computing environment 100 includes a data center 150, astorage appliance 140, and a computing device 154 in communication witheach other via one or more networks 180. The networked computingenvironment 100 may include a plurality of computing devicesinterconnected through one or more networks 180. The one or morenetworks 180 may allow computing devices and/or storage devices toconnect to and communicate with other computing devices and/or otherstorage devices. In some cases, the networked computing environment mayinclude other computing devices and/or other storage devices not shown.The other computing devices may include, for example, a mobile computingdevice, a non-mobile computing device, a server, a workstation, a laptopcomputer, a tablet computer, a desktop computer, or an informationprocessing system. The other storage devices may include, for example, astorage area network storage device, a networked-attached storagedevice, a hard disk drive, a solid-state drive, or a data storagesystem. The one or more networks 180 may include a cellular network, amobile network, a wireless network, a wired network, a secure networksuch as an enterprise private network, an unsecure network such as awireless open network, a local area network (LAN), a wide area network(WAN), and the Internet.

The data center 150 may include one or more servers, such as server 160,in communication with one or more storage devices, such as storagedevice 156. The one or more servers may also be in communication withone or more storage appliances, such as storage appliance 170. Theserver 160, storage device 156, and storage appliance 170 may be incommunication with each other via a networking fabric connecting serversand data storage units within the data center to each other. The server160 may comprise a production hardware server. The storage appliance 170may include a data management system for backing up virtual machines,real machines, virtual disks, real disks, and/or electronic files withinthe data center 150. The server 160 may be used to create and manage oneor more virtual machines associated with a virtualized infrastructure.The one or more virtual machines may run various applications, such as adatabase application or a web server. The storage device 156 may includeone or more hardware storage devices for storing data, such as a harddisk drive (HDD), a magnetic tape drive, a solid-state drive (SSD), astorage area network (SAN) storage device, or a networked-attachedstorage (NAS) device. In some cases, a data center, such as data center150, may include thousands of servers and/or data storage devices incommunication with each other. The data storage devices may comprise atiered data storage infrastructure (or a portion of a tiered datastorage infrastructure). The tiered data storage infrastructure mayallow for the movement of data across different tiers of a data storageinfrastructure between higher-cost, higher-performance storage devices(e.g., solid-state drives and hard disk drives) and relativelylower-cost, lower-performance storage devices (e.g., magnetic tapedrives).

A server, such as server 160, may allow a client to download informationor files (e.g., executable, text, application, audio, image, or videofiles) from the server or to perform a search query related toparticular information stored on the server. In some cases, a server mayact as an application server or a file server. In general, a server mayrefer to a hardware device that acts as the host in a client-serverrelationship or a software process that shares a resource with orperforms work for one or more clients. One embodiment of server 160includes a network interface 165, processor 166, memory 167, disk 168,and virtualization manager 169 all in communication with each other.Network interface 165 allows server 160 to connect to one or morenetworks 180. Network interface 165 may include a wireless networkinterface and/or a wired network interface. Processor 166 allows server160 to execute computer readable instructions stored in memory 167 inorder to perform processes described herein. Processor 166 may includeone or more processing units, such as one or more CPUs and/or one ormore GPUs. Memory 167 may comprise one or more types of memory (e.g.,RAM, SRAM, DRAM, EEPROM, Flash, etc.). Disk 168 may include a hard diskdrive and/or a solid-state drive. Memory 167 and disk 168 may comprisehardware storage devices.

The virtualization manager 169 may manage a virtualized infrastructureand perform management operations associated with the virtualizedinfrastructure. For example, the virtualization manager 169 may managethe provisioning of virtual machines running within the virtualizedinfrastructure and provide an interface to computing devices interactingwith the virtualized infrastructure. The virtualization manager 169 mayalso perform various virtual machine related tasks, such as cloningvirtual machines, creating new virtual machines, monitoring the state ofvirtual machines, moving virtual machines between physical hosts forload balancing purposes, and facilitating backups of virtual machines.

One embodiment of storage appliance 170 includes a network interface175, processor 176, memory 177, and disk 178 all in communication witheach other. Network interface 175 allows storage appliance 170 toconnect to one or more networks 180. Network interface 175 may include awireless network interface and/or a wired network interface. Processor176 allows storage appliance 170 to execute computer readableinstructions stored in memory 177 in order to perform processesdescribed herein. Processor 176 may include one or more processingunits, such as one or more CPUs and/or one or more GPUs. Memory 177 maycomprise one or more types of memory (e.g., RAM, SRAM, DRAM, EEPROM, NORFlash, NAND Flash, etc.). Disk 178 may include a hard disk drive and/ora solid-state drive. Memory 177 and disk 178 may comprise hardwarestorage devices.

In one embodiment, the storage appliance 170 may include four machines.Each of the four machines may include a multi-core CPU, 64 GB of RAM, a400 GB SSD, three 4 TB HDDs, and a network interface controller. In thiscase, the four machines may be in communication with the one or morenetworks 180 via the four network interface controllers. The fourmachines may comprise four nodes of a server cluster. The server clustermay comprise a set of physical machines that are connected together viaa network. The server cluster may be used for storing data associatedwith a plurality of virtual machines, such as backup data associatedwith different point in time versions of one or more virtual machines.

In another embodiment, the storage appliance 170 may comprise a virtualappliance that comprises four virtual machines. Each of the virtualmachines in the virtual appliance may have 64 GB of virtual memory, a 12TB virtual disk, and a virtual network interface controller. In thiscase, the four virtual machines may be in communication with the one ormore networks 180 via the four virtual network interface controllers.The four virtual machines may comprise four nodes of a virtual cluster.

The networked computing environment 100 may provide a cloud computingenvironment for one or more computing devices. In one embodiment, thenetworked computing environment 100 may include a virtualizedinfrastructure that provides software, data processing, and/or datastorage services to end users accessing the services via the networkedcomputing environment. In one example, networked computing environment100 may provide cloud-based work productivity or business relatedapplications to a computing device, such as computing device 154. Thecomputing device 154 may comprise a mobile computing device or a tabletcomputer. The storage appliance 140 may comprise a cloud-based datamanagement system for backing up virtual machines and/or files within avirtualized infrastructure, such as virtual machines running on server160 or files stored on server 160.

In some embodiments, the storage appliance 170 may manage the extractionand storage of virtual machine snapshots associated with different pointin time versions of one or more virtual machines running within the datacenter 150. A snapshot of a virtual machine may correspond with a stateof the virtual machine at a particular point in time. In some cases, thesnapshot may capture the state of various virtual machine settings andthe state of one or more virtual disks for the virtual machine. Inresponse to a restore command from the server 160, the storage appliance170 may restore a point in time version of a virtual machine or restorepoint in time versions of one or more files located on the virtualmachine and transmit the restored data to the server 160. In response toa mount command from the server 160, the storage appliance 170 may allowa point in time version of a virtual machine to be mounted and allow theserver 160 to read and/or modify data associated with the point in timeversion of the virtual machine. To improve storage density, the storageappliance 170 may deduplicate and compress data associated withdifferent versions of a virtual machine and/or deduplicate and compressdata associated with different virtual machines. To improve systemperformance, the storage appliance 170 may first store virtual machinesnapshots received from a virtualized environment in a cache, such as aflash-based cache. The cache may also store popular data or frequentlyaccessed data (e.g., based on a history of virtual machinerestorations), incremental files associated with commonly restoredvirtual machine versions, and current day incremental files orincremental files corresponding with snapshots captured within the past24 hours.

An incremental file may comprise a forward incremental file or a reverseincremental file. A forward incremental file may include a set of datarepresenting changes that have occurred since an earlier point in timesnapshot of a virtual machine. To generate a snapshot of the virtualmachine corresponding with a forward incremental file, the forwardincremental file may be combined with an earlier point in time snapshotof the virtual machine (e.g., the forward incremental file may becombined with the last full image of the virtual machine that wascaptured before the forward incremental was captured and any otherforward incremental files that were captured subsequent to the last fullimage and prior to the forward incremental file). A reverse incrementalfile may include a set of data representing changes from a later pointin time snapshot of a virtual machine. To generate a snapshot of thevirtual machine corresponding with a reverse incremental file, thereverse incremental file may be combined with a later point in timesnapshot of the virtual machine (e.g., the reverse incremental file maybe combined with the most recent snapshot of the virtual machine and anyother reverse incremental files that were captured prior to the mostrecent snapshot and subsequent to the reverse incremental file).

The storage appliance 170 may provide a user interface (e.g., aweb-based interface or a graphical user interface) that displays virtualmachine information, such as identifications of the virtual machinesprotected and the historical versions or time machine views for each ofthe virtual machines protected, and allows an end user to search,select, and control virtual machines managed by the storage appliance. Atime machine view of a virtual machine may include snapshots of thevirtual machine over a plurality of points in time. Each snapshot maycomprise the state of the virtual machine at a particular point in time.Each snapshot may correspond with a different version of the virtualmachine (e.g., Version 1 of a virtual machine may correspond with thestate of the virtual machine at a first point in time and Version 2 ofthe virtual machine may correspond with the state of the virtual machineat a second point in time subsequent to the first point in time).

FIG. 1B depicts one embodiment of server 160 in FIG. 1A. The server 160may comprise one server out of a plurality of servers that are networkedtogether within a data center. In one example, the plurality of serversmay be positioned within one or more server racks within the datacenter. As depicted, the server 160 includes hardware-level componentsand software-level components. The hardware-level components include oneor more processors 182, one or more memory 184, and one or more disks185. The software-level components include a hypervisor 186, avirtualized infrastructure manager 199, and one or more virtualmachines, such as virtual machine 198. The hypervisor 186 may comprise anative hypervisor or a hosted hypervisor. The hypervisor 186 may providea virtual operating platform for running one or more virtual machines,such as virtual machine 198. Virtual machine 198 includes a plurality ofvirtual hardware devices including a virtual processor 192, a virtualmemory 194, and a virtual disk 195. The virtual disk 195 may comprise afile stored within the one or more disks 185. In one example, a virtualmachine may include a plurality of virtual disks, with each virtual diskof the plurality of virtual disks associated with a different filestored on the one or more disks 185. Virtual machine 198 may include aguest operating system 196 that runs one or more applications, such asapplication 197. The virtualized infrastructure manager 199, which maycorrespond with the virtualization manager 169 in FIG. 1A, may run on avirtual machine or natively on the server 160. The virtualizedinfrastructure manager 199 may provide a centralized platform formanaging a virtualized infrastructure that includes a plurality ofvirtual machines.

In one embodiment, the server 160 may use the virtualized infrastructuremanager 199 to facilitate backups for a plurality of virtual machines(e.g., eight different virtual machines) running on the server 160. Eachvirtual machine running on the server 160 may run its own guestoperating system and its own set of applications. Each virtual machinerunning on the server 160 may store its own set of files using one ormore virtual disks associated with the virtual machine (e.g., eachvirtual machine may include two virtual disks that are used for storingdata associated with the virtual machine).

In one embodiment, a data management application running on a storageappliance, such as storage appliance 140 in FIG. 1A or storage appliance170 in FIG. 1A, may request a snapshot of a virtual machine running onserver 160. The snapshot of the virtual machine may be stored as one ormore files, with each file associated with a virtual disk of the virtualmachine. A snapshot of a virtual machine may correspond with a state ofthe virtual machine at a particular point in time. The particular pointin time may be associated with a time stamp. In one example, a firstsnapshot of a virtual machine may correspond with a first state of thevirtual machine (including the state of applications and files stored onthe virtual machine) at a first point in time (e.g., 6:30 p.m. on Jun.29, 2017) and a second snapshot of the virtual machine may correspondwith a second state of the virtual machine at a second point in timesubsequent to the first point in time (e.g., 6:30 p.m. on Jun. 30,2017).

In response to a request for a snapshot of a virtual machine at aparticular point in time, the virtualized infrastructure manager 199 mayset the virtual machine into a frozen state or store a copy of thevirtual machine at the particular point in time. The virtualizedinfrastructure manager 199 may then transfer data associated with thevirtual machine (e.g., an image of the virtual machine or a portion ofthe image of the virtual machine) to the storage appliance. The dataassociated with the virtual machine may include a set of files includinga virtual disk file storing contents of a virtual disk of the virtualmachine at the particular point in time and a virtual machineconfiguration file storing configuration settings for the virtualmachine at the particular point in time. The contents of the virtualdisk file may include the operating system used by the virtual machine,local applications stored on the virtual disk, and user files (e.g.,images and word processing documents). In some cases, the virtualizedinfrastructure manager 199 may transfer a full image of the virtualmachine to the storage appliance or a plurality of data blockscorresponding with the full image (e.g., to enable a full image-levelbackup of the virtual machine to be stored on the storage appliance). Inother cases, the virtualized infrastructure manager 199 may transfer aportion of an image of the virtual machine associated with data that haschanged since an earlier point in time prior to the particular point intime or since a last snapshot of the virtual machine was taken. In oneexample, the virtualized infrastructure manager 199 may transfer onlydata associated with changed blocks stored on a virtual disk of thevirtual machine that have changed since the last snapshot of the virtualmachine was taken. In one embodiment, the data management applicationmay specify a first point in time and a second point in time and thevirtualized infrastructure manager 199 may output one or more changeddata blocks associated with the virtual machine that have been modifiedbetween the first point in time and the second point in time.

FIG. 1C depicts one embodiment of a storage appliance, such as storageappliance 170 in FIG. 1A. The storage appliance may include a pluralityof physical machines that may be grouped together and presented as asingle computing system. Each physical machine of the plurality ofphysical machines may comprise a node in a cluster (e.g., a failovercluster). As depicted, the storage appliance 170 includes hardware-levelcomponents and software-level components. The hardware-level componentsinclude one or more physical machines, such as physical machine 120 andphysical machine 130. The physical machine 120 includes a networkinterface 121, processor 122, memory 123, and disk 124 all incommunication with each other. Processor 122 allows physical machine 120to execute computer readable instructions stored in memory 123 toperform processes described herein. Disk 124 may include a hard diskdrive and/or a solid-state drive. The physical machine 130 includes anetwork interface 131, processor 132, memory 133, and disk 134 all incommunication with each other. Processor 132 allows physical machine 130to execute computer readable instructions stored in memory 133 toperform processes described herein. Disk 134 may include a hard diskdrive and/or a solid-state drive. In some cases, disk 134 may include aflash-based SSD or a hybrid HDD/SSD drive. In one embodiment, thestorage appliance 170 may include a plurality of physical machinesarranged in a cluster (e.g., eight machines in a cluster). Each of theplurality of physical machines may include a plurality of multi-coreCPUs, 128 GB of RAM, a 500 GB SSD, four 4 TB HDDs, and a networkinterface controller.

As depicted in FIG. 1C, the software-level components of the storageappliance 170 may include data management system 102, a virtualizationinterface 104, a distributed job scheduler 108, a distributed metadatastore 110, a distributed file system 112, and one or more virtualmachine search indexes, such as virtual machine search index 106. In oneembodiment, the software-level components of the storage appliance 170may be run using a dedicated hardware-based appliance. In anotherembodiment, the software-level components of the storage appliance 170may be run from the cloud (e.g., the software-level components may beinstalled on a cloud service provider).

In some cases, the data storage across a plurality of nodes in a cluster(e.g., the data storage available from the one or more physicalmachines) may be aggregated and made available over a single file systemnamespace (e.g., /snapshots/). A directory for each virtual machineprotected using the storage appliance 170 may be created (e.g., thedirectory for Virtual Machine A may be /snapshots/VM_A). Snapshots andother data associated with a virtual machine may reside within thedirectory for the virtual machine. In one example, snapshots of avirtual machine may be stored in subdirectories of the directory (e.g.,a first snapshot of Virtual Machine A may reside in /snapshots/VM_A/s1/and a second snapshot of Virtual Machine A may reside in/snapshots/VM_A/s2/).

The distributed file system 112 may present itself as a single filesystem, in which as new physical machines or nodes are added to thestorage appliance 170, the cluster may automatically discover theadditional nodes and automatically increase the available capacity ofthe file system for storing files and other data. Each file stored inthe distributed file system 112 may be partitioned into one or morechunks. Each of the one or more chunks may be stored within thedistributed file system 112 as a separate file. The files stored withinthe distributed file system 112 may be replicated or mirrored over aplurality of physical machines, thereby creating a load-balanced andfault tolerant distributed file system. In one example, storageappliance 170 may include ten physical machines arranged as a failovercluster and a first file corresponding with a full-image snapshot of avirtual machine (e.g., /snapshots/VM_A/s1/s1.full) may be replicated andstored on three of the ten machines. In some cases, the data chunksassociated with a file stored in the distributed file system 112 mayinclude replicated data (e.g., due to n-way mirroring) or parity data(e.g., due to erasure coding). When a disk storing one of the datachunks fails, then the distributed file system may regenerate the lostdata and store the lost data using a new disk.

In one embodiment, the distributed file system 112 may be used to storea set of versioned files corresponding with a virtual machine. The setof versioned files may include a first file comprising a full image ofthe virtual machine at a first point in time and a second filecomprising an incremental file relative to the full image. The set ofversioned files may correspond with a snapshot chain for the virtualmachine. The distributed file system 112 may determine a first set ofdata chunks that includes redundant information for the first file(e.g., via application of erasure code techniques) and store the firstset of data chunks across a plurality of nodes within a cluster. Theplacement of the first set of data chunks within the cluster may bedetermined based on the locations of other data related to the first setof data chunks (e.g., the locations of other chunks corresponding withthe second file or other files within the snapshot chain for the virtualmachine). In some embodiments, the distributed file system 112 may alsoco-locate data chunks or replicas of virtual machines discovered to besimilar to each other in order to allow for cross virtual machinededuplication. In this case, the placement of the first set of datachunks may be determined based on the locations of other datacorresponding with a different virtual machine that has been determinedto be sufficiently similar to the virtual machine.

The distributed metadata store 110 may comprise a distributed databasemanagement system that provides high availability without a single pointof failure. The distributed metadata store 110 may act as a quick-accessdatabase for various components in the software stack of the storageappliance 170 and may store metadata corresponding with stored snapshotsusing a solid-state storage device, such as a solid-state drive (SSD) ora Flash-based storage device. In one embodiment, the distributedmetadata store 110 may comprise a database, such as a distributeddocument oriented database. The distributed metadata store 110 may beused as a distributed key value storage system. In one example, thedistributed metadata store 110 may comprise a distributed NoSQL keyvalue store database. In some cases, the distributed metadata store 110may include a partitioned row store, in which rows are organized intotables or other collections of related data held within a structuredformat within the key value store database. A table (or a set of tables)may be used to store metadata information associated with one or morefiles stored within the distributed file system 112. The metadatainformation may include the name of a file, a size of the file, filepermissions associated with the file, when the file was last modified,and file mapping information associated with an identification of thelocation of the file stored within a cluster of physical machines. Inone embodiment, a new file corresponding with a snapshot of a virtualmachine may be stored within the distributed file system 112 andmetadata associated with the new file may be stored within thedistributed metadata store 110. The distributed metadata store 110 mayalso be used to store a backup schedule for the virtual machine and alist of snapshots for the virtual machine that are stored using thestorage appliance 170.

In some cases, the distributed metadata store 110 may be used to manageone or more versions of a virtual machine. The concepts described hereinmay also be applicable to managing versions of a real machine orversions of electronic files. Each version of the virtual machine maycorrespond with a full image snapshot of the virtual machine storedwithin the distributed file system 112 or an incremental snapshot of thevirtual machine (e.g., a forward incremental or reverse incremental)stored within the distributed file system 112. In one embodiment, theone or more versions of the virtual machine may correspond with aplurality of files. The plurality of files may include a single fullimage snapshot of the virtual machine and one or more incrementalsderived from the single full image snapshot. The single full imagesnapshot of the virtual machine may be stored using a first storagedevice of a first type (e.g., a HDD) and the one or more incrementalsderived from the single full image snapshot may be stored using a secondstorage device of a second type (e.g., an SSD). In this case, only asingle full image needs to be stored and each version of the virtualmachine may be generated from the single full image or the single fullimage combined with a subset of the one or more incrementals.Furthermore, each version of the virtual machine may be generated byperforming a sequential read from the first storage device (e.g.,reading a single file from a HDD) to acquire the full image and, inparallel, performing one or more reads from the second storage device(e.g., performing fast random reads from an SSD) to acquire the one ormore incrementals. In some cases, a first version of a virtual machinecorresponding with a first snapshot of the virtual machine at a firstpoint in time may be generated by concurrently reading a full image forthe virtual machine corresponding with a state of the virtual machineprior to the first point in time from the first storage device whilereading one or more incrementals from the second storage devicedifferent from the first storage device (e.g., reading the full imagefrom a HDD at the same time as reading 64 incrementals from an SSD).

The distributed job scheduler 108 may comprise a distributed faulttolerant job scheduler, in which jobs affected by node failures arerecovered and rescheduled to be run on available nodes. In oneembodiment, the distributed job scheduler 108 may be fully decentralizedand implemented without the existence of a master node. The distributedjob scheduler 108 may run job scheduling processes on each node in acluster or on a plurality of nodes in the cluster and each node mayindependently determine which tasks to execute. The distributed jobscheduler 108 may be used for scheduling backup jobs that acquire andstore virtual machine snapshots for one or more virtual machines overtime. The distributed job scheduler 108 may follow a backup schedule tobackup an entire image of a virtual machine at a particular point intime or one or more virtual disks associated with the virtual machine atthe particular point in time.

The job scheduling processes running on at least a plurality of nodes ina cluster (e.g., on each available node in the cluster) may manage thescheduling and execution of a plurality of jobs. The job schedulingprocesses may include run processes for running jobs, cleanup processesfor cleaning up failed tasks, and rollback processes for rolling-back orundoing any actions or tasks performed by failed jobs. In oneembodiment, the job scheduling processes may detect that a particulartask for a particular job has failed and in response may perform acleanup process to clean up or remove the effects of the particular taskand then perform a rollback process that processes one or more completedtasks for the particular job in reverse order to undo the effects of theone or more completed tasks. Once the particular job with the failedtask has been undone, the job scheduling processes may restart theparticular job on an available node in the cluster.

The virtualization interface 104 may provide an interface forcommunicating with a virtualized infrastructure manager managing avirtualized infrastructure, such as the virtualized infrastructuremanager 199 in FIG. 1B, and for requesting data associated with virtualmachine snapshots from the virtualized infrastructure. Thevirtualization interface 104 may communicate with the virtualizedinfrastructure manager using an API for accessing the virtualizedinfrastructure manager (e.g., to communicate a request for a snapshot ofa virtual machine).

The virtual machine search index 106 may include a list of files thathave been stored using a virtual machine and a version history for eachof the files in the list. Each version of a file may be mapped to theearliest point in time snapshot of the virtual machine that includes theversion of the file or to a snapshot of the virtual machine thatincludes the version of the file (e.g., the latest point in timesnapshot of the virtual machine that includes the version of the file).In one example, the virtual machine search index 106 may be used toidentify a version of the virtual machine that includes a particularversion of a file (e.g., a particular version of a database, aspreadsheet, or a word processing document). In some cases, each of thevirtual machines that are backed up or protected using storage appliance170 may have a corresponding virtual machine search index.

The data management system 102 may comprise an application running onthe storage appliance that manages the capturing, storing,deduplication, compression (e.g., using a lossless data compressionalgorithm such as LZ4 or LZ77), and encryption (e.g., using a symmetrickey algorithm such as Triple DES or AES-256) of data for the storageappliance 170. In one example, the data management system 102 maycomprise a highest level layer in an integrated software stack runningon the storage appliance. The integrated software stack may include thedata management system 102, the virtualization interface 104, thedistributed job scheduler 108, the distributed metadata store 110, andthe distributed file system 112. In some cases, the integrated softwarestack may run on other computing devices, such as a server or computingdevice 154 in FIG. 1A. The data management system 102 may use thevirtualization interface 104, the distributed job scheduler 108, thedistributed metadata store 110, and the distributed file system 112 tomanage and store one or more snapshots of a virtual machine. Eachsnapshot of the virtual machine may correspond with a point in timeversion of the virtual machine. The data management system 102 maygenerate and manage a list of versions for the virtual machine. Eachversion of the virtual machine may map to or reference one or morechunks and/or one or more files stored within the distributed filesystem 112. Combined together, the one or more chunks and/or the one ormore files stored within the distributed file system 112 may comprise afull image of the version of the virtual machine.

In some embodiments, a plurality of versions of a virtual machine may bestored as a base file associated with a complete image of the virtualmachine at a particular point in time and one or more incremental filesassociated with forward and/or reverse incremental changes derived fromthe base file. The data management system 102 may patch together thebase file and the one or more incremental files in order to generate aparticular version of the plurality of versions by adding and/orsubtracting data associated with the one or more incremental files fromthe base file or intermediary files derived from the base file. In someembodiments, each version of the plurality of versions of a virtualmachine may correspond with a merged file. A merged file may includepointers or references to one or more files and/or one or more chunksassociated with a particular version of a virtual machine. In oneexample, a merged file may include a first pointer or symbolic link to abase file and a second pointer or symbolic link to an incremental fileassociated with the particular version of the virtual machine. In someembodiments, the one or more incremental files may correspond withforward incrementals (e.g., positive deltas), reverse incrementals(e.g., negative deltas), or a combination of both forward incrementalsand reverse incrementals.

FIG. 1D depicts one embodiment of a portion of an integrated datamanagement and storage system that includes a plurality of nodes incommunication with each other and one or more storage devices via one ormore networks 180. The plurality of nodes may be networked together andpresent themselves as a unified storage system. The plurality of nodesincludes node 141 and node 147. The one or more storage devices includestorage device 157 and storage device 158. Storage device 157 maycorrespond with a cloud-based storage (e.g., private or public cloudstorage). Storage device 158 may comprise a hard disk drive (HDD), amagnetic tape drive, a solid-state drive (SSD), a storage area network(SAN) storage device, or a networked-attached storage (NAS) device. Theintegrated data management and storage system may comprise a distributedcluster of storage appliances in which each of the storage appliancesincludes one or more nodes. In one embodiment, node 141 and node 147 maycomprise two nodes housed within a first storage appliance, such asstorage appliance 170 in FIG. 1C. In another embodiment, node 141 maycomprise a first node housed within a first storage appliance and node147 may comprise a second node housed within a second storage appliancedifferent from the first storage appliance. The first storage applianceand the second storage appliance may be located within a data center,such as data center 150 in FIG. 1A, or located within different datacenters.

As depicted, node 141 includes a network interface 142, a nodecontroller 143, and a first plurality of storage devices including HDDs144-145 and SSD 146. The first plurality of storage devices may comprisetwo or more different types of storage devices. The node controller 143may comprise one or more processors configured to store, deduplicate,compress, and/or encrypt data stored within the first plurality ofstorage devices. Node 147 includes a network interface 148, a nodecontroller 149, and a second plurality of storage devices including HDDs151-152 and SSD 153. The second plurality of storage devices maycomprise two or more different types of storage devices. The nodecontroller 149 may comprise one or more processors configured to store,deduplicate, compress, and/or encrypt data stored within the secondplurality of storage devices. In some cases, node 141 may correspondwith physical machine 120 in FIG. 1C and node 147 may correspond withphysical machine 130 in FIG. 1C.

FIGS. 2A-2K depict various embodiments of sets of files and datastructures (e.g., implemented using merged files) associated withmanaging and storing snapshots of virtual machines. Although variousembodiments may be described in reference to the management of virtualmachine snapshots, the concepts may be applied to the management ofother data snapshots as well, such as snapshots of databases, filesets(e.g., Network Attached Storage filesets), and sets of electronic files.

FIG. 2A depicts one embodiment of a set of virtual machine snapshotsstored as a first set of files. The first set of files may be storedusing a distributed file system, such as distributed file system 112 inFIG. 1C. As depicted, the first set of files includes a set of reverseincrementals (R1-R4), a full image (Base), and a set of forwardincrementals (F1-F2). The set of virtual machine snapshots includesdifferent versions of a virtual machine (versions V1-V7 of VirtualMachine A) captured at different points in time (times T1-T7). In somecases, the file size of the reverse incremental R3 and the file size ofthe forward incremental F2 may both be less than the file size of thebase image corresponding with version V5 of Virtual Machine A. The baseimage corresponding with version V5 of Virtual Machine A may comprise afull image of Virtual Machine A at point in time T5. The base image mayinclude a virtual disk file for Virtual Machine A at point in time T5.The reverse incremental R3 corresponds with version V2 of VirtualMachine A and the forward incremental F2 corresponds with version V7 ofVirtual Machine A. The forward incremental F1 may be associated with thedata changes that occurred to Virtual Machine A between time T5 and timeT6 and may comprise one or more changed data blocks.

In some embodiments, each snapshot of the set of virtual machinesnapshots may be stored within a storage appliance, such as storageappliance 170 in FIG. 1A. In other embodiments, a first set of the setof virtual machine snapshots may be stored within a first storageappliance and a second set of the set of virtual machine snapshots maybe stored within a second storage appliance, such as storage appliance140 in FIG. 1A. In this case, a data management system may extend acrossboth the first storage appliance and the second storage appliance. Inone example, the first set of the set of virtual machine snapshots maybe stored within a local cluster repository (e.g., recent snapshots ofthe file may be located within a first data center) and the second setof the set of virtual machine snapshots may be stored within a remotecluster repository (e.g., older snapshots or archived snapshots of thefile may be located within a second data center) or a cloud repository.

FIG. 2B depicts one embodiment of a merged file for generating versionV7 of Virtual Machine A using the first set of files depicted in FIG.2A. The merged file includes a first pointer (pBase) that references thebase image Base (e.g., via the path /snapshots/VM_A/s5/s5.full), asecond pointer (pF1) that references the forward incremental F1 (e.g.,via the path /snapshots/VM_A/s6/s6.delta), and a third pointer (pF2)that references the forward incremental F2 (e.g., via the path/snapshots/VM_A/s7/s7.delta). In one embodiment, to generate the fullimage of version V7 of Virtual Machine A, the base image may beacquired, the data changes associated with forward incremental F1 may beapplied to (or patched to) the base image to generate an intermediateimage, and then the data changes associated with forward incremental F2may be applied to the intermediate image to generate the full image ofversion V7 of Virtual Machine A.

FIG. 2C depicts one embodiment of a merged file for generating versionV2 of Virtual Machine A using the first set of files depicted in FIG.2A. The merged file includes a first pointer (pBase) that references thebase image Base (e.g., via the path /snapshots/VM_A/s5/s5.full), asecond pointer (pR1) that references the reverse incremental R1 (e.g.,via the path /snapshots/VM_A/s4/s4.delta), a third pointer (pR2) thatreferences the reverse incremental R2 (e.g., via the path/snapshots/VM_A/s3/s3.delta), and a fourth pointer (pR3) that referencesthe reverse incremental R3 (e.g., via the path/snapshots/VM_A/s2/s2.delta). In one embodiment, to generate the fullimage of version V2 of Virtual Machine A, the base image may beacquired, the data changes associated with reverse incremental R1 may beapplied to the base image to generate a first intermediate image, thedata changes associated with reverse incremental R2 may be applied tothe first intermediate image to generate a second intermediate image,and then the data changes associated with reverse incremental R3 may beapplied to the second intermediate image to generate the full image ofversion V2 of Virtual Machine A.

FIG. 2D depicts one embodiment of a set of virtual machine snapshotsstored as a second set of files after a rebasing process has beenperformed using the first set of files in FIG. 2A. The second set offiles may be stored using a distributed file system, such as distributedfile system 112 in FIG. 1C. The rebasing process may generate new filesR12, R11, and Base2 associated with versions V5-V7 of Virtual Machine Ain order to move a full image closer to a more recent version of VirtualMachine A and to improve the reconstruction time for the more recentversions of Virtual Machine A. The data associated with the full imageBase in FIG. 2A may be equivalent to the new file R12 patched over R11and the full image Base2. Similarly, the data associated with the fullimage Base2 may be equivalent to the forward incremental F2 in FIG. 2Apatched over F1 and the full image Base in FIG. 2A.

The process of moving the full image snapshot for the set of virtualmachine snapshots to correspond with the most recent snapshot versionmay be performed in order to shorten or reduce the chain lengths for thenewest or most recent snapshots, which may comprise the snapshots ofVirtual Machine A that are the most likely to be accessed. In somecases, a rebasing operation (e.g., that moves the full image snapshotfor a set of virtual machine snapshots to correspond with the mostrecent snapshot version) may be triggered when a number of forwardincremental files is greater than a threshold number of forwardincremental files for a snapshot chain (e.g., more than 200 forwardincremental files). In other cases, a rebasing operation may betriggered when the total disk size for the forward incremental filesexceeds a threshold disk size (e.g., is greater than 200 GB) or isgreater than a threshold percentage (e.g., is greater than 20%) of thebase image for the snapshot chain.

In some cases, the rebasing process may be part of a periodic rebasingprocess that is applied at a rebasing frequency (e.g., every 24 hours)to each virtual machine of a plurality of protected virtual machines toreduce the number of forward incremental files that need to be patchedto a base image in order to restore the most recent version of a virtualmachine. Periodically reducing the number of forward incremental filesmay reduce the time to restore the most recent version of the virtualmachine as the number of forward incremental files that need to beapplied to a base image to generate the most recent version may belimited. In one example, if a rebasing process is applied to snapshotsof a virtual machine every 24 hours and snapshots of the virtual machineare acquired every four hours, then the number of forward incrementalfiles may be limited to at most five forward incremental files.

As depicted, the second set of files includes a set of reverseincrementals (R11-R12 and R1-R4) and a full image (Base2). The set ofvirtual machine snapshots includes the different versions of the virtualmachine (versions V1-V7 of Virtual Machine A) captured at the differentpoints in time (times T1-T7) depicted in FIG. 2A. In some cases, thefile size of the reverse incremental R2 may be substantially less thanthe file size of the base image Base2. The reverse incremental R2corresponds with version V2 of Virtual Machine A and the base imageBase2 corresponds with version V7 of Virtual Machine A. In this case,the most recent version of Virtual Machine A (i.e., the most recentrestore point for Virtual Machine A) comprises a full image. To generateearlier versions of Virtual Machine A, reverse incrementals may beapplied to (or patched to) the full image Base2. Subsequent versions ofVirtual Machine A may be stored as forward incrementals that depend fromthe full image Base2.

In one embodiment, a rebasing process may be applied to a first set offiles associated with a virtual machine in order to generate a secondset of files to replace the first set of files. The first set of filesmay include a first base image from which a first version of the virtualmachine may be derived and a first forward incremental file from which asecond version of the virtual machine may be derived. The second set offiles may include a second reverse incremental file from which the firstversion of the virtual machine may be derived and a second base imagefrom which the second version of the virtual machine may be derived.During the rebasing process, data integrity checking may be performed todetect and correct data errors in the files stored in a file system,such as distributed file system 112 in FIG. 1C, that are read togenerate the second set of files.

FIG. 2E depicts one embodiment of a merged file for generating versionV7 of Virtual Machine A using the second set of files depicted in FIG.2D. The merged file includes a first pointer (pBase2) that referencesthe base image Base2 (e.g., via the path /snapshots/VM_A/s7/s7.full). Inthis case, the full image of version V7 of Virtual Machine A may bedirectly acquired without patching forward incrementals or reverseincrementals to the base image Base2 corresponding with version V7 ofVirtual Machine A.

FIG. 2F depicts one embodiment of a merged file for generating versionV2 of Virtual Machine A using the second set of files depicted in FIG.2D. The merged file includes a first pointer (pBase2) that referencesthe base image Base2 (e.g., via the path /snapshots/VM_A/s7/s7.full), asecond pointer (pR11) that references the reverse incremental R11 (e.g.,via the path /snapshots/VM_A/s6/s6.delta), a third pointer (pR12) thatreferences the reverse incremental R12 (e.g., via the path/snapshots/VM_A/s5/s5.delta), a fourth pointer (pR1) that references thereverse incremental R1 (e.g., via the path /snapshots/VM_A/s4/s4.delta),a fifth pointer (pR2) that references the reverse incremental R2 (e.g.,via the path /snapshots/VM_A/s3/s3.delta), and a sixth pointer (pR3)that references the reverse incremental R3 (e.g., via the path/snapshots/VM_A/s2/s2.delta). In one embodiment, to generate the fullimage of version V2 of Virtual Machine A, the base image may beacquired, the data changes associated with reverse incremental R11 maybe applied to the base image to generate a first intermediate image, thedata changes associated with reverse incremental R12 may be applied tothe first intermediate image to generate a second intermediate image,the data changes associated with reverse incremental R1 may be appliedto the second intermediate image to generate a third intermediate image,the data changes associated with reverse incremental R2 may be appliedto the third intermediate image to generate a fourth intermediate image,and then the data changes associated with reverse incremental R3 may beapplied to the fourth intermediate image to generate the full image ofversion V2 of Virtual Machine A.

FIG. 2G depicts one embodiment of a set of files associated withmultiple virtual machine snapshots. The set of files may be stored usinga distributed file system, such as distributed file system 112 in FIG.1C. As depicted, the set of files includes a second full image (BaseB),a set of forward incrementals (F1-F2 and F5-F6) that derive from thesecond full image (BaseB), and a set of reverse incrementals (R1-R3)that derive from the second full image (BaseB). The set of files alsoincludes a first full image (BaseA) and a reverse incremental (R4) thatderives from the first full image (BaseA). In this case, the depictedsnapshots for Virtual Machine A include two different full imagesnapshots (BaseA and BaseB). Each of the full image snapshots maycomprise an anchor snapshot for a snapshot chain. The first full image(BaseA) and the reverse incremental (R4) may comprise a first snapshotchain with the first full image acting as the anchor snapshot. A secondsnapshot chain may comprise the second full image (BaseB) acting as theanchor snapshot for the second snapshot chain, the set of forwardincrementals (F1-F2), and the set of reverse incrementals (R1-R3). Thefirst snapshot chain and the second snapshot chain may be independent ofeach other and independently managed. For example, the base imageassociated with the second snapshot chain for Virtual Machine A may berepositioned (e.g., via rebasing) without impacting the first snapshotchain for Virtual Machine A.

A third snapshot chain for Virtual Machine C may comprise the secondfull image (BaseB) and forward incrementals (F1 and F5-F6). The firstsnapshot chain for Virtual Machine A and the third snapshot chain forVirtual Machine C may be independent of each other and independentlymanaged. However, as Virtual Machine C is a dependent virtual machinethat depends from the second snapshot chain for Virtual Machine A,changes to the second snapshot chain may impact the third snapshotchain. For example, repositioning of the base image for the secondsnapshot chain due to rebasing may require the merged files for thethird snapshot chain to be updated.

In some embodiments, each of the snapshot chains for Virtual Machine Amay have a maximum incremental chain length (e.g., no more than 100total incremental files), a maximum reverse incremental chain length(e.g., no more than 50 reverse incremental files), and a maximum forwardincremental chain length (e.g., no more than 70 forward incrementalfiles. In the event that a new snapshot will cause one of the snapshotchains to violate the maximum incremental chain length, the maximumreverse incremental chain length, or the maximum forward incrementalchain length, then a new snapshot chain may be created for VirtualMachine A and a new full-image base file may be stored for the newsnapshot chain.

FIG. 2H depicts one embodiment of a merged file for generating versionVS of Virtual Machine A using the set of files depicted in FIG. 2G. Themerged file includes a first pointer (pBaseA) that references the firstbase image BaseA and a second pointer (pR4) that references the reverseincremental R4. In one embodiment, to generate the full image of versionVS of Virtual Machine A, the first base image associated with Version VTof Virtual Machine A may be acquired and the data changes associatedwith reverse incremental R4 may be applied to the first base image togenerate the full image of version VS of Virtual Machine A.

FIG. 2I depicts one embodiment of a merged file for generating versionVU of Virtual Machine A using the set of files depicted in FIG. 2G. Themerged file includes a first pointer (pBaseB) that references the secondbase image BaseB, a second pointer (pR1) that references the reverseincremental R1, a third pointer (pR2) that references the reverseincremental R2, and a fourth pointer (pR3) that references the reverseincremental R3. In one embodiment, to generate the full image of versionVU of Virtual Machine A, the second base image associated with VersionVY of Virtual Machine A may be acquired, the data changes associatedwith reverse incremental R1 may be applied to the second base image togenerate a first intermediate image, the data changes associated withreverse incremental R2 may be applied to the first intermediate image togenerate a second intermediate image, and the data changes associatedwith reverse incremental R3 may be applied to the second intermediateimage to generate the full image of version VU of Virtual Machine A.

FIG. 2J depicts one embodiment of a set of files associated withmultiple virtual machine snapshots after a rebasing process has beenperformed to a snapshot chain using the set of files in FIG. 2G. The setof files may be stored using a distributed file system, such asdistributed file system 112 in FIG. 1C. The rebasing process maygenerate new files R12, R11, and BaseB2. As depicted, the set of filesincludes a set of reverse incrementals (R11-R12 and R1-R2), a full image(BaseB2), and a set of forward incrementals (F5-F7). In this case, asecond version of Virtual Machine C may be generated using forwardincrementals F5-F6 that are derived from Version VZ of Virtual MachineA. Forward incremental file F7 may include changes to Version VW ofVirtual Machine A that occurred subsequent to the generation of the fullimage file BaseB2. In some cases, the forward incremental file F7 maycomprise a writeable file or have file permissions allowing modificationof the file, while all other files associated with earlier versions ofVirtual Machine A comprise read only files.

FIG. 2K depicts one embodiment of a merged file for generating versionVU of Virtual Machine A using the set of files depicted in FIG. 2J. Themerged file includes a first pointer (pBaseA) that references the firstbase image BaseA and a second pointer (pF9) that references the forwardincremental F9. In one embodiment, to generate the full image of versionVU of Virtual Machine A, the first base image associated with Version VTof Virtual Machine A may be acquired and the data changes associatedwith forward incremental F9 may be applied to the first base image togenerate the full image of version VU of Virtual Machine A.

In some embodiments, upon detection that a second snapshot chain hasreached a maximum incremental chain length (e.g., no more than 500 totalincremental files), a maximum reverse incremental chain length (e.g., nomore than 400 reverse incremental files), or a maximum forwardincremental chain length (e.g., no more than 150 forward incrementalfiles), an existing snapshot chain (e.g., the first snapshot chaindepicted in FIG. 2J) may have its chain length extended or snapshotspreviously assigned to the second snapshot chain may be moved to theexisting snapshot chain. For example, the first snapshot chain depictedin FIG. 2G comprises two total snapshots, while the first snapshot chaindepicted in FIG. 2J comprises three total snapshots as the snapshotcorresponding with version VU of Virtual Machine A has moved from thesecond snapshot chain to the first snapshot chain.

In some embodiments, the number of snapshots in a snapshot chain maydecrease over time as older versions of a virtual machine areconsolidated, archived, deleted, or moved to a different storage domain(e.g., to cloud storage) depending on the data backup and archivingschedule for the virtual machine. In some cases, the maximum incrementalchain length or the maximum number of snapshots for a snapshot chain maybe increased over time as the versions stored by the snapshot chain age.In one example, if the versions of a virtual machine stored using asnapshot chain are all less than one month old, then the maximumincremental chain length may be set to a maximum of 200 incrementals;however, if the versions of the virtual machine stored using thesnapshot chain are all greater than one month old, then the maximumincremental chain length may be set to a maximum of 1000 incrementals.

In some embodiments, the maximum incremental chain length for a snapshotchain may be increased over time as the number of allowed snapshots in asnapshot chain may be increased as the backed-up versions of a virtualmachine get older. For example, the maximum incremental chain length fora snapshot chain storing versions of a virtual machine that are lessthan one year old may comprise a maximum incremental chain length of 200incrementals, while the maximum incremental chain length for a snapshotchain storing versions of a virtual machine that are more than one yearold may comprise a maximum incremental chain length of 500 incrementals.

FIG. 3A is a flowchart describing one embodiment of a process formanaging and storing virtual machine snapshots using a data storagesystem. In one embodiment, the process of FIG. 3A may be performed by astorage appliance, such as storage appliance 170 in FIG. 1A.

In step 302, a schedule for backing up a first virtual machine isdetermined. In one example, the schedule for backing up the firstvirtual machine may comprise periodically backing up the first virtualmachine every four hours. The schedule for backing up the first virtualmachine may be derived from a new backup, replication, and archivalpolicy or backup class assigned to the first virtual machine. In step304, a job scheduler is configured to implement the schedule for backingup the first virtual machine. In one example, a distributed jobscheduler, such as distributed job scheduler 108 in FIG. 1C, may beconfigured to schedule and run processes for capturing and storingimages of the first virtual machine over time according the schedule. Instep 306, a snapshot process for acquiring a snapshot of the firstvirtual machine is initiated. The snapshot process may send aninstruction to a virtualized infrastructure manager, such asvirtualization manager 169 in FIG. 1A, that requests data associatedwith the snapshot of the first virtual machine. In step 308, a type ofsnapshot to be stored is determined. The type of snapshot may comprise afull image snapshot or an incremental snapshot. In some cases, a fullimage snapshot may be captured and stored in order to serve as an anchorsnapshot for a new snapshot chain. Versions of the first virtual machinemay be stored using one or more independent snapshot chains, whereineach snapshot chain comprises a full image snapshot and one or moreincremental snapshots. One embodiment of a process for determining thetype of snapshot to be stored (e.g., storing either a full imagesnapshot or an incremental snapshot) is described later in reference toFIG. 3B.

In step 310, it is determined whether a full image of the first virtualmachine needs to be stored in order to store the snapshot of the firstvirtual machine. The determination of whether a full image is requiredmay depend on whether a previous full image associated with a priorversion of the first virtual machine has been acquired. Thedetermination of whether a full image is required may depend on thedetermination of the type of snapshot to be stored in step 308. If afull image needs to be stored, then step 311 is performed. Otherwise, ifa full image does not need to be stored, then step 312 is performed. Instep 311, the full image of the first virtual machine is acquired. Thefull image of the first virtual machine may correspond with a file orone or more data chunks. In step 312, changes relative to a priorversion of the first virtual machine or relative to another virtualmachine (e.g., in the case that the first virtual machine comprises adependent virtual machine whose snapshots derive from a full imagesnapshot of a second virtual machine different from the first virtualmachine) are acquired. The changes relative to the prior version of thefirst virtual machine or relative to a version of a different virtualmachine may correspond with a file or one or more data chunks. In step313, the full image of the first virtual machine is stored using adistributed file system, such as distributed file system 112 in FIG. 1C.In step 314, the changes relative to the prior version of the firstvirtual machine or relative to another virtual machine are stored usinga distributed file system, such as distributed file system 112 in FIG.1C. In one embodiment, the full image of the first virtual machine maybe stored using a first storage device of a first type (e.g., a HDD) andthe changes relative to the prior version of the first virtual machinemay be stored using a second storage device of a second type (e.g., anSSD).

In some embodiments, snapshots of the first virtual machine may beingested at a snapshot capture frequency (e.g., every 30 minutes) by adata storage system. When a snapshot of the first virtual machine isingested, the snapshot may be compared with other snapshots storedwithin the data storage system in order to identify a candidate snapshotfrom which the snapshot may depend. In one example, a scalableapproximate matching algorithm may be used to identify the candidatesnapshot whose data most closely matches the data associated with thesnapshot or to identify the candidate snapshot whose data has the fewestnumber of data differences with the snapshot. In another example, anapproximate matching algorithm may be used to identify the candidatesnapshot whose data within a first portion of the candidate snapshotmost closely matches data associated with a first portion of thesnapshot. In some cases, a majority of the data associated with thesnapshot and the candidate snapshot may be identical (e.g., both thesnapshot and the candidate snapshot may be associated with virtualmachines that use the same operating system and have the sameapplications installed). Once the candidate snapshot has beenidentified, then data differences (or the delta) between the snapshotand the candidate snapshot may be determined and the snapshot may bestored based on the data differences. In one example, the snapshot maybe stored using a forward incremental file that includes the datadifferences between the snapshot and the candidate snapshot. The forwardincremental file may be compressed prior to being stored within a filesystem, such as distributed file system 112 in FIG. 1C.

In step 316, a merged file associated with the snapshot is generated.The merged file may reference one or more files or one or more datachunks that have been acquired in either step 311 or step 312. In oneexample, the merged file may comprise a file or a portion of a file thatincludes pointers to the one or more files or the one or more datachunks. In step 318, the merged file is stored in a metadata store, suchas distributed metadata store 110 in FIG. 1C. In step 320, a virtualmachine search index for the first virtual machine is updated. Thevirtual machine search index for the first virtual machine may include alist of files that have been stored in the first virtual machine and aversion history for each of the files in the list. In one example, thevirtual machine search index for the first virtual machine may beupdated to include new files that have been added to the first virtualmachine since a prior snapshot of the first virtual machine was takenand/or to include updated versions of files that were previously storedin the first virtual machine.

FIG. 3B is a flowchart describing one embodiment of a process fordetermining the type of snapshot to be stored using a data storagesystem. The process described in FIG. 3B is one example of a process forimplementing step 308 in FIG. 3A. In one embodiment, the process of FIG.3B may be performed by a storage appliance, such as storage appliance170 in FIG. 1A.

In step 332, a snapshot chain for a first virtual machine is identified.The snapshot chain may comprise a full image snapshot for the firstvirtual machine and one or more incremental snapshots that derive fromthe full image snapshot. Backed-up versions of the first virtual machinemay correspond with one or more snapshot chains. Each of the one or moresnapshot chains may include a full image snapshot or a base image fromwhich incremental snapshots may derive.

In step 334, it is determined whether the snapshot chain includes adependent base file. In this case, the first virtual machine maycomprise a dependent virtual machine that has snapshots that derive froma full image snapshot of a different virtual machine. In one embodiment,the first virtual machine and the different virtual machine from whichthe first virtual machine depends may each have different virtualmachine configuration files for storing configuration settings for thevirtual machines. In one example, the first virtual machine may have afirst number of virtual processors (e.g., two processors) and thedifferent virtual machine may have a second number of virtual processorsdifferent from the first number of virtual processors (e.g., fourprocessors). In another example, the first virtual machine may have afirst virtual memory size (e.g., 1 GB) and the different virtual machinemay have a second virtual memory size different from the first virtualmemory size (e.g., 2 GB). In another example, the first virtual machinemay run a first guest operating system and the different virtual machinemay run a second guest operating system different from the first guestoperating system.

In step 336, a maximum incremental chain length for the snapshot chainis determined based on whether the snapshot chain includes a dependentbase file. In one example, if the first virtual machine comprises adependent virtual machine, then the maximum incremental chain length maybe set to a maximum length of 200 snapshots; however if the firstvirtual machine is independent and is not a dependent virtual machine,then the maximum incremental chain length may be set to a maximum lengthof 500 snapshots.

In one embodiment, the maximum incremental chain length for the snapshotchain may be determined based on an age of the backed-up versions withinthe snapshot chain. In one example, the maximum incremental chain lengthfor a snapshot chain storing versions of the first virtual machine thatare less than one year old may comprise a maximum incremental chainlength of 100 incrementals, while the maximum incremental chain lengthfor a snapshot chain storing versions of the first virtual machine thatare more than one year old may comprise a maximum incremental chainlength of 200 incrementals.

In step 338, it is determined whether a new snapshot chain should becreated based on the maximum incremental chain length. In step 340, atype of snapshot to be stored for the first virtual machine isdetermined based on the maximum incremental chain length. The type ofsnapshot may comprise either a full image snapshot or an incrementalsnapshot. In one embodiment, if the snapshot chain for the first virtualmachine exceeds the maximum incremental chain length for the snapshotchain, then the type of snapshot to be stored for the first virtualmachine may comprise a full image snapshot. In this case, an additionalsnapshot chain may be created for the first virtual machine.

In some embodiments, the number of snapshots in a snapshot chain maydecrease over time as older versions of a virtual machine areconsolidated, archived, deleted, or moved to a different storage domain(e.g., to cloud storage) depending on the data backup and archivingschedule for the virtual machine. In some cases, the maximum incrementalchain length or the maximum number of snapshots for a snapshot chain maybe increased over time as the versions stored by the snapshot chain age.In one example, if the versions of a virtual machine stored using asnapshot chain are all less than one month old, then the maximumincremental chain length may be set to a maximum of 200 incrementals;however, if the versions of the virtual machine stored using thesnapshot chain are all greater than one month old, then the maximumincremental chain length may be set to a maximum of 1000 incrementals.

FIG. 3C is a flowchart describing one embodiment of a process forrestoring a version of a virtual machine using a data storage system. Inone embodiment, the process of FIG. 3C may be performed by a storageappliance, such as storage appliance 170 in FIG. 1A.

In step 382, a particular version of a virtual machine to be restored isidentified. In step 384, a base image from which the particular versionmay be derived is determined. In step 386, a set of incremental filesfor generating the particular version is determined. In one embodiment,the base image and the set of incremental files may be determined from amerged file associated with the particular version of the virtualmachine. In some cases, the set of incremental files may include one ormore forward incremental files and/or one or more reverse incrementalfiles. In step 388, a file associated with the particular version isgenerated using the base image and the set of incremental files. Thefile may be generated by patching the set of incremental files onto thebase image. In step 390, at least a portion of the file is outputted.The at least a portion of the file may be electronically transferred toa computing device, such as computing device 154 in FIG. 1A, or to avirtualization manager, such as virtualization manager 169 in FIG. 1A.

In some embodiments, the base image and a subset of the set ofincremental files may correspond with a second virtual machine differentfrom the virtual machine. In this case, the base image may comprise thebase image for the second virtual machine and the set of incrementalfiles may include a dependent base file that comprises data differencesbetween the base image for the second virtual machine and a previouslyacquired base image for the virtual machine.

FIG. 4A depicts one embodiment of sets of electronic files for capturingdifferent point in time versions of protected data, such as a fileset ora virtual machine. The sets of electronic files may be stored using adistributed file system, such as distributed file system 112 in FIG. 1C.As depicted, a first set of files corresponding with a snapshot chainincludes a set of reverse incrementals (R1-R4), a full image 402 (Base),and a set of forward incrementals (F1-F2). The different point in timeversions of the virtual machine (versions V1-V7 of Virtual Machine VM)were captured and stored using the first set of files. The first set offiles may be partitioned or split into two or more snapshot sub-chainsor shard chains. As depicted, the full image 402 (Base) may bepartitioned into a first full image 404 (BaseA) and a second full image406 (BaseB). In one example, the full image 402 may comprise anelectronic file of size 1 TB, the first full image 404 may comprise anelectronic file of size 500 GB, and the second full image 406 maycomprise an electronic file of 500 GB. In another example, the fullimage 402 may comprise an electronic file of size 1 TB, the first fullimage 404 may comprise an electronic file of size 800 GB, and the secondfull image 406 may comprise an electronic file of 200 GB. Thepartitioning of the full image 402 may create a plurality of uniformlysized base images or a plurality of base images corresponding with aplurality of snapshot sub-chains that have uniform maximum data sizes ornon-uniform maximum data sizes.

As depicted in FIG. 4A, a second set of files corresponding with a firstsnapshot sub-chain includes a set of reverse incrementals (RA1-RA4), afull image 404 (BaseA), and a set of forward incrementals (FA1-FA2). Athird set of files corresponding with a second snapshot sub-chainincludes a set of reverse incrementals (RB1-RB4), a full image 406(BaseB), and a set of forward incrementals (FB1-FB2). The differentpoint in time versions of the virtual machine (versions V1-V7 of VirtualMachine VM) may be generated and outputted using the second set of filescorresponding with the first snapshot sub-chain and the third set offiles corresponding with the second snapshot sub-chain.

In some cases, a first set of operations (e.g., reverse, consolidate,rebase, read, and/or write operations) may be performed on the secondset of files corresponding with the first snapshot sub-chainindependently of a second set of operations being performed on the thirdset of files corresponding with the second snapshot sub-chain. The firstset of operations may comprise snapshot chain manipulation operations,such as a reverse operation or a consolidation operation, that generatenew files for a snapshot chain or a snapshot sub-chain. In one example,the full image 404 may be read in parallel with the full image 406. Inanother example, a first rebasing operation may be performed on thefirst snapshot sub-chain while a second rebasing operation may beperformed on the second snapshot sub-chain. In this case, the firstrebasing operation may generate a new first base image for the firstsnapshot sub-chain and the second rebasing operation may generate a newsecond base image for the second snapshot sub-chain. The generated baseimages may be aligned such that the new first base image may correspondwith a particular version of the virtual machine (e.g., Version V7 ofthe Virtual Machine VM) and the new second base image may correspondwith the particular version of the virtual machine. In some cases, thegenerated base images may not be aligned such that the new first baseimage may correspond with a particular version of the virtual machine(e.g., Version V7 of the Virtual Machine VM) and the new second baseimage may correspond with a different version of the virtual machine(e.g., Version V6 of the Virtual Machine VM).

In some embodiments, the determination of whether to convert or splitthe first set of files corresponding with the snapshot chain into thesecond set of files corresponding with the first snapshot sub-chain andthe third set of files corresponding with the second snapshot sub-chainmay depend upon the detection of one or more triggering conditions. Thetriggering conditions may include detection that the amount of availabledisk space has fallen below a threshold amount of available disk space(e.g., has fallen below or is less than 20 TB), detection that there hasbeen a change in snapshot frequency (e.g., the snapshot frequency mayhave changed from capturing snapshots every 6 hours to every 4 hours),detection that the total number of snapshots captured for the virtualmachine is greater than a threshold number (e.g., the total number ofsnapshots has exceeded more than 1000 snapshots or the total number ofpoint in time versions backed-up for the virtual machine has exceededmore than 400 versions), detection that the aggregate file sizes of thefirst set of files has exceeded a threshold file size, and/or detectionthat the amount of disk space required for the first set of files hasexceeded a threshold amount of disk space (e.g., the first set of filesrequires more than 400 GBs of disk space).

FIG. 4B depicts one embodiment of a snapshot chain including a baseimage and one or more incrementals that derive from the base image beingconverted or split into a first snapshot sub-chain 414 and a secondsnapshot sub-chain 416. In some cases, the first snapshot sub-chain 414and the second snapshot sub-chain 416 may have uniform widths or maximumfiles sizes. In one example, the files corresponding with the firstsnapshot sub-chain 414 may have a maximum file size (e.g., files sizesnot greater than 1 TB) and the files corresponding with the secondsnapshot sub-chain 416 may also have the same maximum file size.

FIG. 4C depicts one embodiment of a snapshot chain including a baseimage and one or more incrementals that derive from the base image beingconverted or split into a first snapshot sub-chain 414 and a secondsnapshot sub-chain 416. As depicted, the first snapshot sub-chain 414and the second snapshot sub-chain 416 may have different widths ordifferent maximum files sizes. In one example, the files correspondingwith the first snapshot sub-chain 414 may have a first maximum file size(e.g., files sizes not greater than 1 TB) and the files correspondingwith the second snapshot sub-chain 416 may have a second maximum filesize (e.g., files sizes not greater than 500 GB) different from thefirst maximum file size.

FIG. 4D depicts one embodiment of two snapshot sub-chains 414 and 416being converted into three snapshot sub-chains 417-419. In this case,the first snapshot sub-chain 414 may include a first base image and afirst set of incrementals that derive from the first base image and thesecond snapshot sub-chain 416 include a second base image and a secondset of incrementals that derive from the second base image. The threesnapshot sub-chains 417-419 may include a third snapshot sub-chain 417,a fourth snapshot sub-chain 418, and a fifth snapshot sub-chain 419. Thethird snapshot sub-chain 417 may include a third base image and a thirdset of incremental files that derive from the third base image. Thefourth snapshot sub-chain 418 may include a fourth base image and afourth set of incremental files that derive from the fourth base image.The fifth snapshot sub-chain 419 may include a fifth base image and afifth set of incremental files that derive from the fifth base image.The first base image of the first snapshot sub-chain 414 and the secondbase image of the second snapshot sub-chain 416 may be used to generatea combined base image corresponding with a particular version of avirtual machine. The third base image of the third snapshot sub-chain417, the fourth base image of the fourth snapshot sub-chain 418, and thefifth base image of the fifth snapshot sub-chain 419 may be used to alsogenerate the combined base image corresponding with the particularversion of the virtual machine.

In some embodiments, the determination of whether to increase the numberof snapshot sub-chains (e.g., by converting or splitting two snapshotsub-chains into three snapshot sub-chains) may depend upon the detectionof one or more triggering conditions. The triggering conditions mayinclude detection that the amount of available disk space has fallenbelow a threshold amount of available disk space (e.g., has fallen belowor is less than 10 TB), detection that there has been a change insnapshot frequency (e.g., the snapshot frequency may have changed fromcapturing snapshots every 24 hours to every 4 hours), detection that thetotal number of snapshots captured for the virtual machine has exceededa threshold number (e.g., the total number of snapshots has exceededmore than 1000 snapshots), detection versions), detection that theaggregate file sizes of the snapshots has exceeded a threshold filesize, and/or detection that the amount of disk space required for thesnapshots has exceeded a threshold amount of disk space (e.g., thesnapshots require more than 800 GBs of disk space).

FIG. 4E depicts one embodiment of two snapshot sub-chains 414 and 416being consolidated into a consolidated snapshot chain 422. In this case,the first snapshot sub-chain 414 may include a first base image and afirst set of incrementals that derive from the first base image and thesecond snapshot sub-chain 416 include a second base image and a secondset of incrementals that derive from the second base image. Theconsolidated snapshot chain 422 may include a third base image and athird set of incrementals that derive from the third base image. Thethird base image may be equivalent to the combination of the first baseimage and the second base image. The third base image may correspondwith a full image snapshot of a particular version of a virtual machine.A combination of the first base image and the second base image may alsocorrespond with the full image snapshot of the particular version of thevirtual machine.

In some embodiments, the determination of whether to decrease the numberof snapshot sub-chains (e.g., by consolidating two snapshot sub-chainsinto a single snapshot chain) may depend upon the detection of one ormore triggering conditions. The triggering conditions may includedetection that the amount of available disk space is greater than athreshold amount of available disk space (e.g., has risen to be greaterthan 50 TB), detection that there has been a change in snapshotfrequency (e.g., the snapshot frequency may have changed from capturingsnapshots every 4 hours to every 24 hours), and/or detection that thetotal number of backed-up versions for the virtual machine is less thana threshold number (e.g., due to consolidation of previously capturedsnapshots of the virtual machine, the total number of back-up versionsfor the virtual machine has fallen below 500 versions of the virtualmachine).

FIG. 4F depicts one embodiment of converting a portion of a snapshotchain into two or more snapshot sub-chains. As depicted, different pointin time versions of a virtual machine have been captured and stored as afirst set of files corresponding with the snapshot chain 422, a secondset of files corresponding with the first snapshot sub-chain 424, and athird set of files corresponding with the second snapshot sub-chain 426.The second set of files corresponding with the first snapshot sub-chain424 and the third set of files corresponding with the second snapshotsub-chain 426 may be converted into the three snapshot sub-chains427-429.

In one embodiment, a portion of a snapshot chain (e.g., correspondingwith the 100 most recent versions of a virtual machine out of 200 totalversions of the virtual machine) may be split into two or moresub-chains. In another embodiment, a first set of backed-up versions ofa virtual machine (e.g., versions V1-V100) may be stored as a first setof files corresponding with a single snapshot chain, such as snapshotchain 422 in FIG. 4F, and a second set of backed-up versions of thevirtual machine (e.g., versions V101-V200) may be stored as filescorresponding with two or more snapshot sub-chains, such as snapshotsub-chains 424 and 426 in FIG. 4F. Upon detection that an amount ofavailable disk space for a cluster has fallen below a threshold amountof disk space, the two or more snapshot sub-chains may be converted intothree or more snapshot sub-chains, such as snapshot sub-chains 427-429in FIG. 4F.

In some embodiments, a first set of versions of a virtual machine maycorrespond with a top snapshot chain (e.g., snapshot chain 422 in FIG.4F) and a second set of versions of the virtual machine may correspondwith two or more snapshot sub-chains (e.g., snapshot sub-chains 424 and426 in FIG. 4F). The top snapshot chain may be stored using a storageappliance, such as storage appliance 140 in FIG. 1A, or stored using aremote cluster repository (e.g., older snapshots may be moved to asecond data center) or a cloud repository. The two or more snapshotsub-chains may be stored using the same storage appliance as that usedto store the top snapshot chain. In some cases, the top snapshot chainmay be stored using a remote cluster repository (e.g., located within asecond data center) or a cloud repository and the bottom snapshot chainmay be stored using a local storage appliance.

FIG. 4G depicts one embodiment of consolidating snapshot sub-chainsassociated with a subset of backed-up versions of protected data (e.g.,a virtual machine or a large file set comprising 500K files) into asingle snapshot chain. As depicted, different point in time versions ofa virtual machine have been captured and stored as a first set of filescorresponding with the snapshot chain 422, a second set of filescorresponding with the first snapshot sub-chain 424, and a third set offiles corresponding with the second snapshot sub-chain 426. The secondset of files corresponding with the first snapshot sub-chain 424 and thethird set of files corresponding with the second snapshot sub-chain 426may be consolidated into a single snapshot chain 428.

FIG. 4H depicts one embodiment of consolidating two snapshot chains intoa single snapshot chain. As depicted, a first snapshot chain 422 maycorrespond with a first set of backed-up versions of a virtual machine(e.g., versions V1-V500) and a second snapshot chain 428 may correspondwith a second set of backed-up versions of the virtual machine (e.g.,versions V501-V600). The first snapshot chain 422 and the secondsnapshot chain 428 may be consolidated into a third snapshot chain 430.The third snapshot chain 430 may correspond with both the first set ofbacked-up versions of the virtual machine and the second set ofbacked-up versions of the virtual machine (e.g., versions V1-V600). Thefirst snapshot chain 422 may include a first base image and a first setof incremental files that derive from the first base image. The secondsnapshot chain 428 may include a second base image and a second set ofincremental files that derive from the second base image. The thirdsnapshot chain 430 may include a third base image and a third set ofincremental files that derive from the third base image. In some cases,the total number of electronic files for the third snapshot chain 430may be equal to the number of electronic files for the first snapshotchain 422 plus the number of electronic files for the snapshot chain428. One benefit of consolidating snapshot chains is that the number ofbase images (or full image snapshots) may be reduced.

In some embodiments, different versions of a virtual machine maycorrespond with a top snapshot chain (e.g., snapshot chain 422 in FIG.4H) used for storing a first set of the different versions of thevirtual machine and a bottom snapshot chain (e.g., snapshot chain 428 inFIG. 4H) used for storing a second set of the different versions of thevirtual machine. Upon detection of a triggering event (e.g., the amountof available disk space has fallen below a threshold amount of diskspace due to a node failure), the bottom snapshot chain may be splitinto two or more snapshot sub-chains or both the top snapshot chain andthe bottom snapshot chain may both be split into two or more snapshotsub-chains. In some cases, the top snapshot chain may correspond withthe first snapshot chain depicted in FIG. 2J and the bottom snapshotchain may correspond with the second snapshot chain depicted in FIG. 2J.

FIG. 4I depicts one embodiment of the two snapshot sub-chains of FIG. 4Ain which snapshot sub-chain operations have been independently performedon the two snapshot sub-chains. As depicted, a new base image 436(BaseB2) and two reverse incremental files 437-438 (RB11-RB12) have beengenerated for the second snapshot sub-chain. In this case, a reverseoperation may have been performed using the second snapshot sub-chain inorder to move the base image for the second snapshot sub-chain closer tothe most recent version of the virtual machine comprising version V7.

FIG. 4J depicts one embodiment of four snapshot chains that correspondwith four data partitions comprising a set of electronic files to bebacked-up. The set of electronic files may comprise a fileset and thefour data partitions may comprise the fileset partitioned into fourdifferent data partitions. The snapshot chain (or sub-chain) with fullimage 404 (BaseA) and reverse incremental snapshots corresponding withreverse incremental files 442-443 (RA1 and RA2) depicted in FIG. 4I maycomprise a first snapshot chain for a first partition of the four datapartitions. The snapshot chain with full image 473 (BaseB) may comprisea second snapshot chain for a second partition of the four datapartitions. The snapshot chain with full image 474 (BaseC) may comprisea third snapshot chain for a third partition of the four datapartitions. The snapshot chain with full image 475 (BaseD) may comprisea fourth snapshot chain for a fourth partition of the four datapartitions. As depicted, the four base images for the four datapartitions have been staggered such that the full image 404 (BaseA)corresponds with Version V5 of the first snapshot chain, the full image473 (BaseB) corresponds with Version V6 of the second snapshot chain,the full image 474 (BaseC) corresponds with Version V7 of the thirdsnapshot chain, and the full image 475 (BaseD) corresponds with VersionV8 of the fourth snapshot chain. The four base images may be acquiredfrom a hardware server, such as server 160 in FIG. 1A, or generated by astorage appliance, such as storage appliance 170 in FIG. 1A, at fourdifferent points in time in order to limit the computational and storagedemands placed on the hardware server or the storage appliance.

FIG. 5A depicts one embodiment of four snapshot chains correspondingwith a set of electronic files that have been partitioned into fourdifferent data partitions. The four data partitions comprise a firstdata partition PartitionA, a second data partition PartitionB, a thirddata partition PartitionC, and a fourth data partition PartitionD. Thefirst snapshot chain of the four snapshot chains includes a first fullimage snapshot 502 and forward incremental snapshots 522-525. The secondsnapshot chain of the four snapshot chains includes a second full imagesnapshot 503, a reverse incremental snapshot 513, and a forwardincremental snapshot 514. In some cases, the incremental snapshot 513may comprise a forward incremental snapshot that derives from apreviously acquired full image snapshot not depicted; in this case, theincremental snapshot 513 would be part of a different snapshot chainwith the previously acquired full image snapshot as the anchor snapshot.The third snapshot chain of the four snapshot chains includes a thirdfull image snapshot 504 and the fourth snapshot chain of the foursnapshot chains includes a fourth full image snapshot 505. The point intime version for the set of electronic files at time T1 may correspondwith a first version of the set of electronic files. Similarly, thepoint in time version for the set of electronic files at time T2 maycorrespond with a second version of the set of electronic files and thepoint in time version for the set of electronic files at time T3 maycorrespond with a third version of the set of electronic files.Therefore, the full image snapshots for the four snapshot chains havebeen staggered over the point in time versions of the set of electronicfiles. In one embodiment, the staggering of the four snapshot chains maybe triggered upon detection that at least one of the snapshot chains hasreached a triggering snapshot chain length that is less than a maximumsnapshot chain length equal to C minus Ceil(1/P), wherein C is themaximum snapshot chain length and P is the maximum percentage of thepartitions for which full image snapshots may be concurrently acquiredand/or generated.

FIG. 5B depicts one embodiment of four snapshot chains correspondingwith a set of electronic files that have been partitioned into fourdifferent data partitions. The first snapshot chain of the four snapshotchains includes a first full image snapshot 502 and forward incrementalsnapshots 522-525. The second snapshot chain includes a second fullimage snapshot 533 and a forward incremental snapshot 514. The thirdsnapshot chain of the four snapshot chains includes a third full imagesnapshot 504 and the fourth snapshot chain of the four snapshot chainsincludes a fourth full image snapshot 535. As depicted, the full imagesnapshots 502 and 533 correspond with a first point in time version ofthe set of electronic files at time T1 and the full image snapshots 504and 535 corresponds with a third point in time version of the set ofelectronic files at time T3. Therefore, the full image snapshots 502 and533 have been staggered from the full image snapshots 504 and 535. Inone embodiment, the full image snapshots 502 and 504 may be acquiredfrom a hardware server, such as server 160 in FIG. 1A, and the fullimage snapshots 533 and 535 may be generated using a storage appliance,such as storage appliance 170 in FIG. 1A. In another embodiment, thefull image snapshots 502 and 504 may be acquired from a hardware serverand the full image snapshots 533 and 535 may also be acquired from thehardware server.

FIG. 5C depicts one embodiment of the first snapshot chain depicted inFIGS. 5A-5B that includes a first full image snapshot 502 and forwardincremental snapshots 522-525. The data partition PartitionA has beenpartitioned into five data blocks comprising Block1 through Block5.Although five data blocks are depicted in FIG. 5C, other embodiments maycomprise less than or more than five data blocks (e.g., a data partitionmay comprise 2000 32 MB data blocks). The incremental snapshots may besharded at the same logical boundaries as the full image snapshot. Asdepicted, the first full image snapshot 502 comprises five data blocks541-545 corresponding with the state of the data blocks Block1 throughBlock5 at time T1, the incremental snapshot 522 comprises data block 551that corresponds with the state of the data block Block1 at time T2, theincremental snapshot 523 comprises the data blocks 552 and 553 thatcorrespond with the states of the data blocks Block1 and Block3 at timeT3, the incremental snapshot 524 comprises the data block 554 thatcorresponds with the state of the data block Block2 at time T4, and theincremental snapshot 525 comprises the data block 555 that correspondswith the state of the data block Block5 at time T5. In order tomaterialize or generate a full image snapshot of the set of electronicfiles at time T3, the data blocks 552-553, 542, and 544-545 must beread; in this case, the data blocks 541 and 543 within the first fullimage snapshot 502 must be replaced with the data blocks 552 and 553.

As depicted in FIG. 5C, the snapshot chain length at time T5 comprisesfour incrementals corresponding with the four incremental snapshots522-525 that need to be applied to the full image snapshot 502 in orderto generate the point in time version of the set of electronic files attime T5. The block chain length for Block1 at time T5 comprises threeblocks as the number of snapshots that need to be read (e.g., startingfrom time T5 and working backwards in time or through prior point intime versions) in order to find the most recent data changes for Block1is three corresponding with the three incremental snapshots 523-525. Theblock chain length for Block2 at time T5 comprises two blocks as thenumber of snapshots that need to be read in order to find the mostrecent data changes for Block2 is two corresponding with the twoincremental snapshots 524-525. Similarly, the block chain length forBlock4 at time T5 comprises five blocks as the number of snapshots thatneed to be read in order to find the most recent data changes for Block4is five corresponding with the four incremental snapshots 522-525 andthe full image snapshot 502. The aggregate block chain length for thefive data blocks at time T5 may comprise 14 blocks comprising the sum ofthe block chain lengths for each of the five data blocks. The aggregateblock chain length may correspond with the number of data block readoperations that need to be performed in order to identify the datablocks for a particular point in time snapshot.

FIG. 5D depicts one embodiment of a snapshot chain in which a secondfull image snapshot 526 has taken the place of the incremental snapshot525 in FIG. 5C. The second full image snapshot 526 may comprise datablocks 561-564 and 555. The data block 561 may comprise a copy of thedata block 552, the data block 562 may comprise a copy of the data block554, the data block 563 may comprise a copy of the data block 553, andthe data block 564 may comprise a copy of the data block 544. In oneembodiment, the second full image snapshot 526 may be acquired orgenerated in response to detecting that the snapshot chain length for apoint in time snapshot of the set of electronic files at time T6 willexceed a threshold snapshot chain length of five. In another embodiment,the second full image snapshot 526 may be acquired or generated inresponse to detecting that the aggregate block chain length at time T6will exceed the maximum aggregate block chain length of 14. In somecases, a first subset of the data blocks comprising the second fullimage snapshot 526 may be acquired from a server while a second subsetof the data blocks comprising the second full image snapshot 526 may begenerated locally using a storage appliance. For example, data blocks561-562 may be acquired from the server while data blocks 563-564 aregenerated using the storage appliance.

FIG. 5E depicts one embodiment of a snapshot chain in which a secondfull image snapshot 562 has been stored corresponding with a point intime version of the set of electronic files at time T6. The second fullimage snapshot 562 may comprise the beginning of a new snapshot chainfor the data partition PartitionA and subsequent incremental snapshotsmay include data changes relative to the second full image snapshot 562.In this case, the second full image snapshot 562 may comprise the anchorsnapshot for the new snapshot chain.

FIG. 5F depicts one embodiment of a snapshot chain with an incrementalsnapshot 563 that includes redundant data blocks. In some cases, ratherthan generating a second full image snapshot, such as the second fullimage snapshot 562 in FIG. 5E, an incremental snapshot with redundantdata blocks may be used to reduce block chain lengths and/or theaggregate block chain length for a data partition. In one example,assuming that data changes only occurred to data within the data blockBlock1 at time T6, then data block 573 may be a copy of data block 553and data block 574 may be a copy of data block 544. Although thesnapshot chain length at time T6 has increased to five incrementals, themaximum block chain length at time T6 has been reduced from five blocksat time T5 in FIG. 5C to three blocks and the aggregate block chainlength at time T6 has been reduced from 14 blocks at time T5 in FIG. 5Cto eight blocks. Thus, the incremental snapshot 563 that includesredundant data blocks has reduced both the maximum block chain lengthand the aggregate block chain length without requiring a full imagesnapshot to be acquired.

FIG. 5G depicts one embodiment of a snapshot chain that includes anincremental snapshot with redundant data blocks. As depicted, a firstdata partition PartitionA may include full image snapshots 582-583 and asecond data partition PartitionB may include full image snapshots584-585 and an incremental snapshot 586 that includes redundant datablocks. The incremental snapshot 586 may correspond with the incrementalsnapshot 563 in FIG. 5F. In one embodiment, the full image snapshots582-583 may be acquired from a server while the full image snapshots584-585 and the incremental snapshot 586 may be generated using astorage appliance. In another embodiment, the full image snapshots584-585 may be acquired from a server and stored using a storageappliance while the incremental snapshot 586 may be generated locallyusing the storage appliance.

FIG. 5H depicts one embodiment of a snapshot chain that includesstaggered full image snapshots and an incremental snapshot withredundant data blocks. As depicted, a first data partition PartitionAmay include full image snapshots 582-583 and a second data partitionPartitionB may include full image snapshots 587-588 and an incrementalsnapshot 586 that includes redundant data blocks. In one embodiment, thedetermination of whether to acquire and/or generate two full imagesnapshots for the data partitions at time T1 may depend on the number offull image snapshots that may be concurrently acquired from a server ornumber of full image snapshots that may be concurrently generated by astorage appliance. In another embodiment, the determination of whetherto stagger the acquisition of full image snapshots 582 and 587 maydepend on a maximum number of full image snapshots that may be acquiredfrom a server for time T1.

FIG. 5I depicts one embodiment in which a data partition PartitionB hasbeen partitioned into two sub-partitions PartitionB1 and PartitionB2. Inthis case, the acquisition and/or generation of full image snapshots 591and 594 may be staggered and the acquisition and/or generation ofincremental snapshots that include redundant blocks 593 and 595 may bestaggered.

FIG. 5J depicts another embodiment in which a data partition PartitionBhas been partitioned into two sub-partitions PartitionB1 andPartitionB2. In this case, the full image snapshot 591 may be acquiredfrom a server while the full image snapshot 596 may be generated locallyusing the storage appliance that stores the different point in timeversions of the set of electronic files. Similarly, the full imagesnapshot 592 may be acquired from the server while the full imagesnapshot 597 may be generated locally using the storage appliance. Theacquisition and/or generation of incremental snapshots that includeredundant blocks 593 and 595 may be staggered. In one example, both ofthe incremental snapshots that include redundant blocks 593 and 595 maybe generated using the storage appliance.

FIG. 6A is a flowchart describing one embodiment of a process foracquiring full image snapshots. In one embodiment, the process of FIG.6A may be performed by a storage appliance, such as storage appliance170 or storage appliance 140 in FIG. 1A. The process of FIG. 6A may beperformed by a data storage node, such as data storage node 141 in FIG.1D.

In step 602, a plurality of files to be backed-up is identified. Theplurality of files may correspond with a virtual machine or a set ofelectronic files. In step 604, a partition size for the plurality offiles is determined. The partition size may depend upon the number ofdata storage nodes in a cluster or the amount of available disk spacewithin the cluster. In step 606, a first partition of the plurality offiles and a second partition of the plurality of files are identifiedbased on the partition size. In one example, the plurality of files maycomprise 20 TBs of data, the first partition may comprise 10 TBs ofdata, and the second partition may comprise 10 TBs of data. In anotherexample, the plurality of files may comprise 20K files, the firstpartition may comprise 10K files, and the second partition may comprise10K files. In step 608, it is detected that an external server is unableto provide both a first full image snapshot for the first partition at afirst point in time and a second full image snapshot for the secondpartition at the first point in time. In some cases, due to networkbandwidth and/or compute resource constraints on the external server atthe first point in time, the external server may only be able to providea single 10 TB full image snapshot.

In step 610, it is determined that acquisition of full image snapshotsof the first partition and the second partition should be staggered. Inone embodiment, it may be determined that the two full image snapshotsshould be staggered in response to detection that the external server isunable to provide both full image snapshots. In another embodiment, itmay be determined that the acquisition of full image snapshots of thefirst partition and the second partition should be staggered if asnapshot chain associated with either the first partition or the secondpartition has reached a triggering snapshot chain length that is lessthan a maximum snapshot chain length.

In step 612, it is detected that the first full image snapshot for thefirst partition at the first point in time should be acquired from theexternal server. In step 614, the first full image snapshot for thefirst partition at the first point in time is acquired and stored. Instep 616, it is detected that a third full image snapshot for the secondpartition at a second point in time subsequent to the first point intime should be acquired from the external server. In step 618, the thirdfull image snapshot for the second partition at the second point in timeis acquired and stored. In one embodiment, the first full image snapshotfor the first partition at the first point in time may correspond withfull image snapshot 582 in FIG. 5H and the third full image snapshot forthe second partition at the second point in time may correspond withfull image snapshot 587 in FIG. 5H.

FIG. 6B is a flowchart describing an alternative embodiment of a processfor acquiring full image snapshots. In one embodiment, the process ofFIG. 6B may be performed by a storage appliance, such as storageappliance 170 or storage appliance 140 in FIG. 1A. The process of FIG.6B may be performed by a data storage node, such as data storage node141 in FIG. 1D.

In step 632, a set of data to be backed-up over time is identified. Theset of data may comprise a virtual machine, one or more virtual disks,or a set of electronic files. In step 634, the set of data ispartitioned into multiple sets of data including a first set of data anda second set of data. In one example, the set of data may correspondwith a set of 10K electronic files, the first set of data may correspondwith a set of 6K electronic files, and the second set of data maycorrespond with a set of 4K electronic files. In step 636, a maximumnumber of data partitions that may be concurrently acquired from anexternal server is determined. The maximum number of data partitions maycorrespond with the maximum number of full image snapshots that may beacquired from the external server for a particular point in timesnapshot of the set of data. In step 638, a maximum number of datapartitions that may be concurrently generated by a storage appliance isdetermined. The maximum number of data partitions that may beconcurrently generated by the storage appliance may correspond with themaximum number of full image snapshots that may be generated by thestorage appliance for a particular point in time snapshot of the set ofdata.

In step 640, it is detected that a first full image snapshot for thefirst set of data at a first point in time should be acquired from theexternal server based on the maximum number of data partitions that maybe concurrently acquired from the external server. In step 642, it isdetected that a second full image snapshot for the second set of data atthe first point in time should be generated by the storage appliancebased on the maximum number of data partitions that may be concurrentlygenerated by the storage appliance. In one embodiment, the first fullimage snapshot for the first set of data at the first point in time maycorrespond with full image snapshot 582 in FIG. 5G and the second fullimage snapshot for the second set of data at the first point in time maycorrespond with full image snapshot 584 in FIG. 5G.

In step 644, the first full image snapshot for the first set of data atthe first point in time is acquired from the external server. In step646, the second full image snapshot for the second set of data at thefirst point in time is generated using the storage appliance. In somecases, the second full image snapshot may be generated by the storageappliance while the first full image snapshot is acquired from theexternal server. In step 648, the first full image snapshot for thefirst set of data at the first point in time and the second full imagesnapshot for the second set of data at the first point in time arestored using the storage appliance.

FIG. 7A is a flowchart describing one embodiment of a process forgenerating full image snapshots. In one embodiment, the process of FIG.7A may be performed by a storage appliance, such as storage appliance170 or storage appliance 140 in FIG. 1A. The process of FIG. 7A may beperformed by a data storage node, such as data storage node 141 in FIG.1D.

In step 702, a plurality of files to be backed-up over time isidentified. The plurality of files may correspond with a set ofelectronic files. In step 704, the plurality of files is partitionedinto two or more sets of files including a first set of files. The firstset of files may be associated with two or more data blocks. In oneexample, the first set of files may correspond with or comprise fivedata blocks, such as the five data blocks Block1 through Block5 in FIG.5E. In step 706, a first full image snapshot of the first set of filescorresponding with a first state of the first set of files at a firstpoint in time is acquired from a server. In step 708, a secondincremental snapshot of the first set of files corresponding with asecond state of the first set of files at a second point in timesubsequent to the first point in time is acquired from the server. Inone embodiment, the first full image snapshot may correspond with fullimage snapshot 502 in FIG. 5E and the second incremental snapshot maycorrespond with incremental snapshot 525 in FIG. 5E.

In step 710, an estimated time for generating a second full imagesnapshot of the first set of files corresponding with the second stateof the first set of files at the second point in time is determinedbased on a state of the two or more data blocks at the second point intime. In one embodiment, the estimated time for generating the secondfull image snapshot of the first set of files corresponding with thesecond state of the first set of files at the second point in time isdetermined based on an aggregate block chain length for the two or moredata blocks of the first set of files at the second point in time. Instep 712, it is detected that the estimated time for generating thesecond full image snapshot of the first set of files is greater than athreshold time (e.g., is greater than two minutes). In step 714, thesecond full image snapshot of the first set of files is generated andstored using a storage appliance in response to detecting that theestimated time is greater than the threshold time.

In one embodiment, upon detection that an aggregate block chain lengthfor the two or more data blocks of the first set of files has exceeded athreshold number of blocks (e.g., is greater than 14 blocks), thestorage appliance may generate and store the second full image snapshotof the first set of files. In another embodiment, upon detection that anaggregate block chain length for the two or more data blocks of thefirst set of files has exceeded a threshold number of blocks, thestorage appliance may generate and store an incremental snapshot thatincludes redundant data blocks, such as the incremental snapshot 563 inFIG. 5F.

In one embodiment, upon detection that the maximum block chain lengthfor the two or more data blocks at the second point in time has exceededa threshold number of blocks (e.g., is greater than five blocks), thestorage appliance may generate and store the second full image snapshotof the first set of files. In another embodiment, upon detection thatthe maximum block chain length for the two or more data blocks at thesecond point in time has exceeded a threshold number of blocks, thestorage appliance may generate and store an incremental snapshot thatincludes redundant data blocks, such as the incremental snapshot 563 inFIG. 5F.

FIG. 7B is a flowchart describing one embodiment of a process forgenerating and storing full image snapshots. In one embodiment, theprocess of FIG. 7B may be performed by a storage appliance, such asstorage appliance 170 or storage appliance 140 in FIG. 1A. The processof FIG. 7B may be performed by a data storage node, such as data storagenode 141 in FIG. 1D.

In step 724, a first partition of files of a set of files is identifiedbased on a partition size for the set of files. The first partition offiles may comprise a plurality of data blocks. In one example, the firstpartition of files may comprise five data blocks, such as the five datablocks Block1 through Block5 in FIG. 5C. In step 726, a first full imagesnapshot of the first partition of files corresponding with a firststate of the first partition of files at a first point in time isacquired from a server. In step 728, a second incremental snapshot ofthe first partition of files corresponding with a second state of thefirst partition of files at a second point in time subsequent to thefirst point in time is acquired from the server. The server maycorrespond with server 160 in FIG. 1A. In one embodiment, the first fullimage snapshot may correspond with full image snapshot 502 in FIG. 5Cand the second incremental snapshot may correspond with incrementalsnapshot 525 in FIG. 5C.

In step 730, an aggregate block chain length for the second incrementalsnapshot of the first partition of files corresponding with the secondstate of the first partition of files at the second point in time isdetermined. In one example, the aggregate block chain length maycomprise the sum of the block chain lengths for each block of theplurality of blocks. In step 732, it is detected that the aggregateblock chain length for the second incremental snapshot is greater than athreshold chain length (e.g., is greater than 14 blocks) or greater thana maximum aggregate block chain length for the first partition of files.In step 734, it is determined whether to generate the second full imagesnapshot or a second incremental snapshot with redundant data blocks. Inone embodiment, the second incremental snapshot with redundant datablocks may be generated if the snapshot chain length is below athreshold length. The second incremental snapshot with redundant datablocks may comprise less than all of the blocks comprising the pluralityof data blocks. The second incremental snapshot with redundant datablocks may comprise a subset of the plurality of data blocks thatcomprises the entirety of the first partition of files. In oneembodiment, the second full image snapshot may correspond with fullimage snapshot 562 in FIG. 5E and the second incremental snapshot withredundant data blocks may correspond with the incremental snapshot 563with redundant data blocks in FIG. 5F. In step 736, one of the secondfull image snapshot of the first partition of files or the secondincremental snapshot with redundant data blocks for the first partitionof files is generated and stored using a storage appliance, such asstorage appliance 170 in FIG. 1A.

FIG. 7C is a flowchart describing one embodiment of a process forgenerating and storing full image snapshots based on an aggregate blockchain length. In one embodiment, the process of FIG. 7C may be performedby a storage appliance, such as storage appliance 170 or storageappliance 140 in FIG. 1A. The process of FIG. 7C may be performed by adata storage node, such as data storage node 141 in FIG. 1D.

In step 752, a first partition of a set of data is identified. The firstpartition may be associated with a plurality of data blocks. In oneembodiment, the first partition may correspond with data partitionPartitionA in FIG. 5F and the plurality of data blocks may correspondwith blocks Block1 through Block5 in FIG. 5F. In step 754, a first fullimage snapshot of the first partition corresponding with a first stateof the first partition at a first point in time is acquired from aserver. In step 756, a second incremental snapshot of the firstpartition corresponding with a second state of the first partition at asecond point in time subsequent to the first point in time is acquiredfrom the server. In step 758, an aggregate block chain length for thesecond incremental snapshot is determined. In some cases, it may bedetected that the aggregate block chain length for the secondincremental snapshot is not greater than a threshold chain length. Instep 760, a third incremental snapshot of the first partitioncorresponding with a third state of the first partition at a third pointin time subsequent to the second point in time is acquired from theserver. In step 762, an aggregate block chain length for the thirdincremental snapshot is determined. In step 764, it is detected that theaggregate block chain length for the third incremental snapshot isgreater than a threshold chain length (or is greater than the maximumaggregate block chain length for incremental snapshots). The aggregateblock chain length for the third incremental snapshot may be greaterthan the aggregate block chain length for the second incrementalsnapshot. In step 766, a second full image snapshot of the firstpartition at the third point in time is generated and stored using astorage appliance.

One embodiment of the disclosed technology includes identifying a set ofdata to be backed-up over time and partitioning the set of data into twoor more sets of data including a first set of data and a second set ofdata. The first set of data is associated with a first snapshot chainand the second set of data is associated with a second snapshot chain.The method further comprises detecting that the first snapshot chain hasreached a triggering snapshot chain length less than a maximum snapshotchain length for the first snapshot chain, determining that acquisitionof full image snapshots for the first set of data and the second set ofdata should be staggered in response to detecting that the firstsnapshot chain has reached the triggering snapshot chain length, andstaggering the acquisition of full image snapshots for the first set ofdata and the second set of data such that a first full image snapshotfor a first point in time version of the first set of data is acquiredfrom a server prior to acquisition of a second full image snapshot for asecond point in time version of the second set of data from the serverand both the first snapshot chain and the second snapshot chain comprisesnapshot chain lengths less than the maximum snapshot chain length. Themethod further comprises storing the first full image snapshot for thefirst point in time version of the first set of data and the second fullimage snapshot for the second point in time version of the second set ofdata using a storage appliance.

One embodiment of the disclosed technology includes identifying a firstdata partition associated with a first snapshot chain. The first datapartition comprises a plurality of data blocks. The method furthercomprises acquiring a first full image snapshot of the first datapartition corresponding with a first state of the first data partitionat a first point in time from a server, acquiring a second incrementalsnapshot of the first data partition corresponding with a second stateof the first data partition at a second point in time subsequent to thefirst point in time from the server, determining an aggregate blockchain length for the second incremental snapshot corresponding with thesecond state of the first data partition at the second point in time,detecting that the aggregate block chain length for the secondincremental snapshot is greater than a threshold chain length,generating one or more data blocks corresponding with the second stateof the first data partition at the second point in time different fromdata blocks of the second incremental snapshot in response to detectingthat the aggregate block chain length for the second incrementalsnapshot is greater than the threshold chain length, and storing the oneor more data blocks and the data blocks of the second incrementalsnapshot.

The disclosed technology may be described in the context ofcomputer-executable instructions, such as software or program modules,being executed by a computer or processor. The computer-executableinstructions may comprise portions of computer program code, routines,programs, objects, software components, data structures, or other typesof computer-related structures that may be used to perform processesusing a computer. In some cases, hardware or combinations of hardwareand software may be substituted for software or used in place ofsoftware.

Computer program code used for implementing various operations oraspects of the disclosed technology may be developed using one or moreprogramming languages, including an object oriented programming languagesuch as Java or C++, a function programming language such as Scala, aprocedural programming language such as the “C” programming language orVisual Basic, or a dynamic programming language such as Python orJavaScript. In some cases, computer program code or machine-levelinstructions derived from the computer program code may execute entirelyon an end user's computer, partly on an end user's computer, partly onan end user's computer and partly on a remote computer, or entirely on aremote computer or server.

For purposes of this document, it should be noted that the dimensions ofthe various features depicted in the Figures may not necessarily bedrawn to scale.

For purposes of this document, reference in the specification to “anembodiment,” “one embodiment,” “some embodiments,” or “anotherembodiment” may be used to describe different embodiments and do notnecessarily refer to the same embodiment.

For purposes of this document, a connection may be a direct connectionor an indirect connection (e.g., via another part). In some cases, whenan element is referred to as being connected or coupled to anotherelement, the element may be directly connected to the other element orindirectly connected to the other element via intervening elements. Whenan element is referred to as being directly connected to anotherelement, then there are no intervening elements between the element andthe other element.

For purposes of this document, the term “based on” may be read as “basedat least in part on.”

For purposes of this document, without additional context, use ofnumerical terms such as a “first” object, a “second” object, and a“third” object may not imply an ordering of objects, but may instead beused for identification purposes to identify different objects.

For purposes of this document, the term “set” of objects may refer to a“set” of one or more of the objects.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. A method for operating a data management system,comprising: identifying a set of data to be backed-up over time;partitioning the set of data into two or more sets of data including afirst set of data and a second set of data, the first set of data isassociated with a first snapshot chain and the second set of data isassociated with a second snapshot chain; detecting that the firstsnapshot chain has reached a triggering snapshot chain length less thana maximum snapshot chain length for the first snapshot chain;determining that acquisition of full image snapshots for the first setof data and the second set of data should be staggered in response todetecting that the first snapshot chain has reached the triggeringsnapshot chain length; staggering the acquisition of full imagesnapshots for the first set of data and the second set of data such thata first full image snapshot for a first point in time version of thefirst set of data is acquired from a server prior to acquisition of asecond full image snapshot for a second point in time version of thesecond set of data from the server and both the first snapshot chain andthe second snapshot chain comprise snapshot chain lengths less than themaximum snapshot chain length; and storing the first full image snapshotfor the first point in time version of the first set of data and thesecond full image snapshot for the second point in time version of thesecond set of data using a storage appliance.
 2. The method of claim 1,wherein: the detecting that the first snapshot chain has reached thetriggering snapshot chain length includes computing the triggeringsnapshot chain length as the maximum snapshot chain length minus onedivided by a maximum percentage of the partitions for which full imagesnapshots may be acquired for a particular point in time version of thetwo or more sets of data.
 3. The method of claim 1, further comprising:detecting that a third full image snapshot corresponding with the firstpoint in time version of the second set of data may be generated by thestorage appliance while the first full image snapshot for the firstpoint in time version of the first set of data is acquired from theserver.
 4. The method of claim 3, further comprising: generating thethird full image snapshot corresponding with the first point in timeversion of the second set of data using the storage appliance; andstoring the third full image snapshot corresponding with the first pointin time version of the second set of data using the storage appliance.5. The method of claim 4, further comprising: detecting that the serveris unable to provide both the first full image snapshot for the firstpoint in time version of the first set of data and the third full imagesnapshot corresponding with the first point in time version of thesecond set of data, the generating the third full image snapshotcorresponding with the first point in time version of the second set ofdata using the storage appliance is performed in response to detectingthat the server is unable to provide both the first full image snapshotfor the first point in time version of the first set of data and thethird full image snapshot corresponding with the first point in timeversion of the second set of data.
 6. The method of claim 5, furthercomprising: determining a maximum number of data partitions that may beconcurrently acquired from the server and detecting that the server isunable to provide both the first full image snapshot for the first pointin time version of the first set of data and the third full imagesnapshot corresponding with the first point in time version of thesecond set of data based on the maximum number of data partitions thatmay be concurrently acquired from the server.
 7. The method of claim 4,further comprising: determining a maximum number of data partitions thatmay be concurrently generated by the storage appliance; detecting thatgeneration of the third full image snapshot corresponding with the firstpoint in time version of the second set of data by the storage appliancesatisfies the maximum number of data partitions that may be concurrentlygenerated by the storage appliance; and generating the third full imagesnapshot corresponding with the first point in time version of thesecond set of data using the storage appliance in response to detectingthat generation of the third full image snapshot corresponding with thefirst point in time version of the second set of data by the storageappliance satisfies the maximum number of data partitions that may beconcurrently generated by the storage appliance.
 8. The method of claim1, further comprising: determining a partition size for the set of databased on an amount of disk space within a cluster of data storage nodesand partitioning the set of data based on the partition size.
 9. Themethod of claim 1, wherein: the set of data comprises a plurality ofelectronic files.
 10. The method of claim 1, wherein: the set of datacomprises a virtual disk.
 11. A data management system, comprising: amemory; and one or more processors in communication with the memoryconfigured to partition a set of data to be protected over time into twoor more sets of data including a first set of data and a second set ofdata, the first set of data is associated with a first snapshot chainand the second set of data is associated with a second snapshot chain,the one or more processors configured to detect that the first snapshotchain has reached a triggering snapshot chain length less than a maximumsnapshot chain length for the first snapshot chain and determine thatacquisition of full image snapshots for the first set of data and thesecond set of data should be staggered in response to detection that thefirst snapshot chain has reached the triggering snapshot chain length,the one or more processors configured to stagger the acquisition of fullimage snapshots for the first set of data and the second set of datasuch that a first full image snapshot for a first point in time versionof the first set of data is acquired from an external server prior toacquisition of a second full image snapshot for a second point in timeversion of the second set of data from the external server and both thefirst snapshot chain and the second snapshot chain comprise snapshotchain lengths less than the maximum snapshot chain length, the one ormore processors configured to cause the first full image snapshot forthe first point in time version of the first set of data and the secondfull image snapshot for the second point in time version of the secondset of data to be stored using the memory.
 12. The data managementsystem of claim 11, wherein: the one or more processors configured tocompute the triggering snapshot chain length as the maximum snapshotchain length minus one divided by a maximum percentage of the partitionsfor which full image snapshots may be acquired for the same point intime version of the set of data.
 13. The data management system of claim11, wherein: the one or more processors configured to detect that athird full image snapshot corresponding with the first point in timeversion of the second set of data may be generated by a storageappliance while the first full image snapshot for the first point intime version of the first set of data is acquired from the externalserver.
 14. The data management system of claim 13, wherein: the one ormore processors configured to generate the third full image snapshotcorresponding with the first point in time version of the second set ofdata using the storage appliance.
 15. The data management system ofclaim 14, wherein: the one or more processors configured to detect thatthe external server is unable to provide both the first full imagesnapshot for the first point in time version of the first set of dataand the third full image snapshot corresponding with the first point intime version of the second set of data; and the one or more processorsconfigured to generate the third full image snapshot corresponding withthe first point in time version of the second set of data in response todetection that the external server is unable to provide both the firstfull image snapshot for the first point in time version of the first setof data and the third full image snapshot corresponding with the firstpoint in time version of the second set of data.
 16. The data managementsystem of claim 15, wherein: the one or more processors configured todetermine a maximum number of data partitions that may be concurrentlyacquired from the external server and detect that the external server isunable to provide both the first full image snapshot for the first pointin time version of the first set of data and the third full imagesnapshot corresponding with the first point in time version of thesecond set of data based on the maximum number of data partitions thatmay be concurrently acquired from the external server.
 17. The datamanagement system of claim 13, wherein: the one or more processorsconfigured to generate the third full image snapshot corresponding withthe first point in time version of the second set of data using thestorage appliance in response to detection that generation of the thirdfull image snapshot corresponding with the first point in time versionof the second set of data by the storage appliance satisfies a maximumnumber of data partitions that may be concurrently generated by thestorage appliance.
 18. The data management system of claim 11, wherein:the one or more processors configured to determine a maximum partitionsize for the set of data based on an amount of disk space within acluster of data storage nodes and partition the set of data based on themaximum partition size.
 19. The data management system of claim 11,wherein: the first set of data comprises a first set of electronicfiles; the second set of data comprises a second set of electronicfiles; and the memory comprises a non-volatile semiconductor memory. 20.One or more storage devices containing processor readable code forprogramming one or more processors to perform a method for operating adata management system, the processor readable code comprising:processor readable code configured to partition a set of files into twoor more sets of files including a first set of files and a second set offiles, the first set of files is associated with a first snapshot chainand the second set of files is associated with a second snapshot chain;processor readable code configured to detect that the first snapshotchain has reached a triggering snapshot chain length less than a maximumsnapshot chain length for the first snapshot chain; processor readablecode configured to determine that acquisition of full image snapshotsfor the first set of files and the second set of files should bestaggered in response to detection that the first snapshot chain hasreached the triggering snapshot chain length; processor readable codeconfigured to stagger the acquisition of full image snapshots for thefirst set of files and the second set of files such that a first fullimage snapshot for a first point in time version of the first set offiles is acquired from an external server prior to acquisition of asecond full image snapshot for a second point in time version of thesecond set of files from the external server and both the first snapshotchain and the second snapshot chain comprise snapshot chain lengths lessthan the maximum snapshot chain length; and processor readable codeconfigured to store the first full image snapshot for the first point intime version of the first set of files and the second full imagesnapshot for the second point in time version of the second set of filesusing a storage appliance.